SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934 

Replidyne, Inc.
(Name of Issuer)

Common Stock, $0.001 par value
(Title of Class of Securities)

76028W107
(CUSIP Number)

July 28, 2006
(Date of Event Which Requires Filing of this Statement)

Check the following box to designate the rule pursuant to which the Schedule is filed:

o
Rule 13d-1(b)
 
x
Rule 13d-1(c)
 
o
Rule 13d-1(d)
 


*The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).
 
 
CUSIP No. 76028W107

1.
Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
 
D. E. Shaw & Co., L.P.
  
 
13-3695715
  
     
2.
Check the Appropriate Box if a Member of a Group (See Instructions)
 
 
(a)
o
 
(b)
o
     
3.
SEC Use Only
 
     
4.
Citizenship or Place of Organization
 
 
Delaware
  
 
Number of
5.
Sole Voting Power
Shares
 
-0-
Beneficially
   
Owned by
6.
Shared Voting Power
Each
 
1,398,200
Reporting
   
Person With
7.
Sole Dispositive Power
   
-0-
     
 
8.
Shared Dispositive Power
   
1,398,200
 
9.
Aggregate Amount Beneficially Owned by Each Reporting Person
  
 
1,398,200
  
     
10.
Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) o
 
    
11.
Percent of Class Represented by Amount in Row (9)
 
 
5.3%
  
     
12.
Type of Reporting Person (See Instructions)
 
 
IA, PN
  


CUSIP No. 76028W107

1.
Names of Reporting Persons. I.R.S. Identification Nos. of above persons (entities only)
 
David E. Shaw
  
     
2.
Check the Appropriate Box if a Member of a Group (See Instructions)
 
 
(a)
o
 
(b)
o
     
3.
SEC Use Only
 
     
4.
Citizenship or Place of Organization
 
 
United States
  
     
 
Number of
5.
Sole Voting Power
Shares
 
-0-
Beneficially
   
Owned by
6.
Shared Voting Power
Each
 
1,398,200
Reporting
   
Person With
7.
Sole Dispositive Power
   
-0-
     
 
8.
Shared Dispositive Power
   
1,398,200
 
9.
Aggregate Amount Beneficially Owned by Each Reporting Person
  
 
1,398,200
  
     
10.
Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions) o
 
    
11.
Percent of Class Represented by Amount in Row (9)
 
 
5.3%
  
     
12.
Type of Reporting Person (See Instructions)
 
 
IN
  



 
Item 1.
 
(a)
Name of Issuer
 
Replidyne, Inc.
   
(b)
Address of Issuer's Principal Executive Offices
 
1450 Infinite Drive
 
Louisville, CO 80027
   
Item 2.
 
(a)
Name of Person Filing
 
D. E. Shaw & Co., L.P.
 
David E. Shaw
   
(b)
Address of Principal Business Office or, if none, Residence
 
The business address for each reporting person is:
 
120 W. 45th Street, Tower 45, 39th Floor
 
New York, NY 10036
   
(c)
Citizenship
 
D. E. Shaw & Co., L.P. is a limited partnership organized under the laws of the state of Delaware.
 
David E. Shaw is a citizen of the United States of America.
   
(d)
Title of Class of Securities
 
Common Stock, $0.001 par value
   
(e)
CUSIP Number
 
76028W107

Item 3. If this statement is filed pursuant to Rule 13d-1(b) or 13d-2(b) or (c), check whether the person filing is a:

Not applicable

Item 4. Ownership.

As of August 2, 2006:

(a) Amount beneficially owned:
  
   
D. E. Shaw & Co., L.P.:
1,398,200 shares
 
This is composed of (i) 1,064,900 shares in the name of D. E. Shaw Meniscus Portfolios, L.L.C. and (ii) 333,300 shares in the name of D. E. Shaw Valence Portfolios, L.L.C.
   
David E. Shaw:
1,398,200 shares
 
This is composed of (i) 1,064,900 shares in the name of D. E. Shaw Meniscus Portfolios, L.L.C. and (ii) 333,300 shares in the name of D. E. Shaw Valence Portfolios, L.L.C.
   
(b) Percent of class:
  
D. E. Shaw & Co., L.P.:
5.3%
David E. Shaw:
5.3%
   
(c) Number of shares to which the person has:
  
(i) Sole power to vote or to direct the vote:
 
D. E. Shaw & Co., L.P.:
-0- shares
David E. Shaw:
-0- shares
   
(ii) Shared power to vote or to direct the vote:
 
D. E. Shaw & Co., L.P.:
1,398,200 shares
David E. Shaw:
1,398,200 shares
   
(iii) Sole power to dispose or to direct the disposition of:
 
D. E. Shaw & Co., L.P.:
-0- shares
David E. Shaw:
-0- shares
   
(iv) Shared power to dispose or to direct the disposition of:
 
D. E. Shaw & Co., L.P.:
1,398,200 shares
David E. Shaw:
1,398,200 shares
 

David E. Shaw does not own any shares directly. By virtue of David E. Shaw’s position as President and sole shareholder of D. E. Shaw & Co., Inc., which is the general partner of D. E. Shaw & Co., L.P., which in turn is the managing member and investment adviser of D. E. Shaw Valence Portfolios, L.L.C. and the investment adviser of D. E. Shaw Meniscus Portfolios, L.L.C., and by virtue of David E. Shaw’s position as President and sole shareholder of D. E. Shaw & Co. II, Inc., which is the managing member of D. E. Shaw & Co., L.L.C., which in turn is the managing member of D. E. Shaw Meniscus Portfolios, L.L.C., David E. Shaw may be deemed to have the shared power to vote or direct the vote of, and the shared power to dispose or direct the disposition of, the 1,398,200 shares as described above constituting 5.3% of the outstanding shares and, therefore, David E. Shaw may be deemed to be the beneficial owner of such shares. David E. Shaw disclaims beneficial ownership of such 1,398,200 shares.
 

Item 5.
Ownership of Five Percent or Less of a Class
Not applicable
 
Item 6.
Ownership of More than Five Percent on Behalf of Another Person.
Not Applicable

Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person.
Not Applicable

Item 8.
Identification and Classification of Members of the Group
Not Applicable

Item 9.
Notice of Dissolution of Group
Not Applicable

Item 10.
Certification
By signing below, each of D. E. Shaw & Co., L.P. and David E. Shaw certify that, to the best of such reporting person’s knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having such purposes or effect.
 


SIGNATURE

After reasonable inquiry and to the best of their knowledge and belief, the undersigned certify that the information set forth in this statement is true, complete and correct. A Power of Attorney, dated February 24, 2004, granted by David E. Shaw in favor of Eric Wepsic, is attached hereto.

Dated: August 7, 2006

D. E. Shaw & Co., L.P.
 
By: /s/ Eric Wepsic
Eric Wepsic
Managing Director


David E. Shaw
 
By: /s/ Eric Wepsic
Eric Wepsic
Attorney-in-Fact for David E. Shaw