| ITEM 1(a). | NAME OF ISSUER: Ironwood Pharmaceuticals, Inc. |
| ITEM 1(b). | ADDRESS OF ISSUER'S PRINCIPAL EXECUTIVE OFFICES: 100 Summer Street, Suite 2300, Boston, MA 02110 |
| ITEM 2(a). | NAME OF PERSON FILING: Westfield Capital Management Company, LP |
| ITEM 2(b). | ADDRESS OF PRINCIPAL BUSINESS OFFICE OR, IF NONE, RESIDENCE: 1 Financial Center, Boston, Massachusetts 02111 |
| ITEM 2(c). | CITIZENSHIP: Massachusetts |
| ITEM 2(d). | TITLE OF CLASS OF SECURITIES: Common Stock |
| ITEM 2(e). | CUSIP NUMBER: 46333X108 |
| ITEM 3. | IF THIS STATEMENT IS FILED PURSUANT TO SECTION 240.13d-1(b), or 13d-2(b) or (c) CHECK WHETHER THE PERSON FILING IS A: |
(a) [ ] | Broker or dealer registered under Section 15 of the Act (15 U.S.C. 78c); |
(b) [ ] | Bank as defined in Section 3(a)(6) of the Act (15 U.S.C. 78c); |
(c) [ ] | Insurance company as defined in Section 3(a)(19) of the Act (15 U.S.C. 78c); |
(d) [ ] | Investment company registered under Section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8); |
(e) [X] | An investment adviser in accordance with 240.13d-1(b)(1)(ii)(E); |
(f) [ ] | An employee benefit plan or endowment fund in accordance with 240.13d-1(b)(1)(ii)(F); |
(g) [ ] | A parent holding company or control person in accordance with 240.13d-1(b)(1)(ii)(G); |
(h) [ ] | A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813); |
(i) [ ] | A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3); |
(j) [ ] | A non-U.S. institution in accordance with 240.13d-1(b)(1)(ii)(J); |
(k) [ ] | Group, in accordance with 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with 240.13d1(b)(1)(ii)(J), please specify the type of institution: |
|
| ITEM 4. | OWNERSHIP |
|
| (a) Amount beneficially owned: |
| 8,145,674 |
| (b) Percent of class: |
| 4.98% |
| (c) Number of shares as to which the person has: |
| (i) sole power to vote or to direct the vote: |
| Westfield Capital Management Company, LP : 7,387,904 |
| (ii) shared power to vote or to direct the vote: |
| Westfield Capital Management Company, LP : 0 |
| (iii) sole power to dispose or direct the disposition of: |
| Westfield Capital Management Company, LP : 8,145,674 |
| (iv) shared power to dispose or to direct the disposition of: |
| Westfield Capital Management Company, LP : 0 |
| ITEM 5. | OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS: If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [X]. |
| 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: 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 I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and 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 that purpose or effect. |
