OBJECTIVE: To determine validity and reliability of the Urdu translated, modified "Response to symptoms questionnaire" (RSQ) among acute coronary syndrome (ACS) patients in Karachi. STUDY DESIGN: A qualitative, tool validation study. PLACE AND DURATION OF STUDY: Two tertiary care hospitals in Karachi, the Aga Khan University Hospital, Karachi and the Karachi Institute of Heart Diseases, from December 2010 to April 2011. METHODOLOGY: After making certain modifications, the original tool in English was translated into Urdu. Next, five cardiology experts evaluated the tool for its content and face validity. Test retest and inter rater reliabilities were computed for the RSQ using 5% of the total sample size of the parent study. RESULTS: Sufficient conceptual and semantic equivalence was found between the Urdu and English versions of the modified RSQ. Content validity index was calculated to be 1 for both relevance and linguistic clarity. Test retest and inter rater reliabilities were calculated to be 95.9% and K = 0.97, respectively. CONCLUSION: The Urdu translated modified RSQ has sufficiently acceptable content validity, test retest and inter rater reliability; hence, it should be used by the researchers for the evaluation of factors associated with pre-hospital delay among Urdu speaking ACS patient populations.