Cognitive assessment is an approach used to evaluate questions in survey interviews. This approach is useful in delineating measurement error due to participants' understanding of terms and interpretation of questions. The purpose of this study was to evaluate the quality of questionnaire items designed to evaluate history of sexually transmitted diseases (STDs) using a cognitive assessment approach. Participants recruited from an STD clinic were asked up to six questions to assess their history of STDs. Verbal probes were used after each question in an attempt to evaluate the participants' understanding of the questions and methods they used to recall episodes of having STDs. The findings revealed that respondents did not understand the medical terms for some STDs, that the wording of one question potentially interfered with respondents' comprehension of the question, and that respondents used an episodic recall method to determine their number of previous STD infections. Cognitive assessment is a useful method for identifying potential sources of respondent-induced measurement error.