EXHIBIT 31.1



CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER PURSUANT TO

SECTION 302(a) OF THE SARBANES-OXLEY ACT OF 2002



I, W. Mark Lortz, certify that:



1. I have reviewed this quarterly report on Form 10-Q of TheraSense, Inc., a Delaware corporation;



2. Based on my knowledge, this report does not contain any untrue statement
of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;



3. Based on my knowledge, the financial statements, and other financial
information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;



4. The registrants other certifying officer(s) and I are responsible
for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:



(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our
supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;



(b) [Paragraph omitted pursuant to SEC
Release Nos. 33-8238 and 34-47986];



(c)
Evaluated the effectiveness of the registrants disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this
report based on such evaluation; and



(d)
Disclosed in this report any change in the registrants internal control over financial reporting that occurred during the registrants most recent fiscal quarter (the registrants fourth fiscal quarter in the case of an annual
report) that has materially affected, or is reasonably likely to materially affect, the registrants internal control over financial reporting; and



5. The registrants other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial
reporting, to the registrants auditors and the audit committee of the registrants board of directors (or persons performing the equivalent functions):



(a) All significant deficiencies and material weaknesses in the design or operation of internal control over
financial reporting which are reasonably likely to adversely affect the registrants ability to record, process, summarize and report financial information; and



(b) Any fraud, whether or not material, that involves management or other employees who have a significant
role in the registrants internal control over financial reporting.



Date: November 13, 2003



| |  | /s/ W. MARK LORTZ      
| |  | -----------------------
| |  | W. Mark Lortz          
| |  | Chief Executive Officer



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I, Charles T. Liamos, certify that:



1. I have reviewed this quarterly report on Form 10-Q of TheraSense, Inc., a Delaware corporation;



2. Based on my knowledge, this report does not contain any untrue statement
of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;



3. Based on my knowledge, the financial statements, and other financial
information included in this report, fairly present in all material respects the financial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;



4. The registrants other certifying officer(s) and I are responsible
for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:



(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our
supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;



(b) [Paragraph omitted pursuant to SEC
Release Nos. 33-8238 and 34-47986];



(c)
Evaluated the effectiveness of the registrants disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of the end of the period covered by this
report based on such evaluation; and



(d)
Disclosed in this report any change in the registrants internal control over financial reporting that occurred during the registrants most recent fiscal quarter (the registrants fourth fiscal quarter in the case of an annual
report) that has materially affected, or is reasonably likely to materially affect, the registrants internal control over financial reporting; and



5. The registrants other certifying officer(s) and I have disclosed, based on our most recent evaluation of internal control over financial
reporting, to the registrants auditors and the audit committee of the registrants board of directors (or persons performing the equivalent functions):



(a) All significant deficiencies and material weaknesses in the design or operation of internal control over
financial reporting which are reasonably likely to adversely affect the registrants ability to record, process, summarize and report financial information; and



(b) Any fraud, whether or not material, that involves management or other employees who have a significant
role in the registrants internal control over financial reporting.



Date: November 13, 2003



| |  | /s/ CHARLES T. LIAMOS  
| |  | -----------------------
| |  | Charles T. Liamos      
| |  | Chief Financial Officer



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