Objectives: To describe the reliability of reported dates of first and last sexual exposure, as elicited from sexually transmitted disease/ human immunodeficiency virus cases during routine contact investigation, and determine their adequacy for assessing concurrency. Methods: We used contact tracing data from 5 studies in which both members of 774 dyads were interviewed and named each other as sex partners. We assessed partners' agreement on the dates of first and last exposure as related to

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... ecision (to the day, month, or year) of reported dates and demographic and behavioral characteristics of the dyad. We performed simulations that introduced reporting error, based on our observed data, to posited "true" temporal configurations of partnerships to assess the impact of unreliability in reporting on the measurement of concurrency. Results: Thirty-two percent of dyads agreed on the exact date of first sexual exposure, and 36% did so for the date of last sexual exposure. Sixty-four percent agreed within 30 days on the date of first sexual exposure, and 81% did so for the date of last sexual exposure. The reliability of reported dates was positively related to the precision of the reports. Agreement on reported exposure dates was not meaningfully associated with any of the sociodemographic and behavioral variables available. Based on simulations, the positive predictive value of reported dates for estimating concurrency is approximately 80% over a wide range of conditions. Conclusions: These data suggest that the reliability of reported exposure dates is reasonably good but that estimating concurrency with reported dates is subject to some error. Data designed for the purpose and analyzed with adequate attention to the statistical and epidemiologic issues of assessing concurrency are needed.