**Exhibit 12.1**

**Certification of Chief Executive Officer**

I, Ronald H.P. Brus,certify that:

1.                            Ihave reviewed this annual report on Form 20-F of Crucell N.V.;

2.                          Based on my knowledge, this report does not containany untrue statement of a material fact or omit to state a material factnecessary to make the statements made, in light of the circumstances underwhich such statements were made, not misleading with respect to the periodcovered by this report;

3.                          Based on my knowledge, the financial statements, andother financial information included in this report, fairly present in allmaterial respects the financial condition, results of operations and cash flowsof the company as of, and for, the periods presented in this report;

4.                          Thecompany’s other certifying officer and I are responsible for establishing andmaintaining disclosure controls andprocedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e))for the company and have:

a)                        Designed such disclosure controls and procedures,or caused such disclosure controls and procedures to be designed under oursupervision, to ensure that material information relating to thecompany, including its consolidated subsidiaries, is made known to us by otherswithin those entities, particularly during the period in which this report isbeing prepared;

b)                       Evaluatedthe effectiveness of the company’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as ofthe end of the period covered by this report based on such evaluation; and

c)                        Disclosedin this report any changes in the company’s internal control over financialreporting that occurred during the period covered by the annual report that hasmaterially affected, or is reasonably likely to materially affect, the company’sinternal control over financial reporting; and

5.                          The company’s othercertifying officer and I have disclosed, based on our most recent evaluation ofinternal control over financial reporting, to the company’sauditors and the audit committee of the company’s board of directors (orpersons performing the equivalent functions):

a)                        All significantdeficiencies and material weaknesses in the design or operation of internal control over financialreporting which are reasonably likely to adversely affect the company’s abilityto record, process, summarize and report financial information; and

b)                       Any fraud, whether or notmaterial, that involves management or other employees who have a significant role in thecompany’s internal control over financial reporting.

 
| Date: June 29, 2006 |   |   |   |                    |
|--------------------------|--------|--------|--------|-------------------------|
|                     |   |   |   |                    |
|                     |   | By:    |   |                    |
|                     |   | Name:  |   | Ronald H.P. Brus        |
|                     |   | Title: |   | Chief Executive Officer |

 

 

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