Introduction and Background: Partner concurrency increases the risk of sexually transmitted infections (STIs) such as Trichomonas vaginalis. Women diagnosed with T. vaginalis have a 2- to 3-fold higher risk of acquiring the human immunodeficiency virus and developing the acquired immunodeficiency syndrome. Goals: We sought to describe partnership concurrency (multiple sexual partners during the same time period) and condom use among women diagnosed with T. vaginalis, and to compare reports of concurrency between matched female and male dyads. Methods: A baseline interview on partnership status and condom use was administered to women diagnosed with T. vaginalis at a public sexually transmitted infections (STI) clinic. A male partner substudy was also conducted. Seventy-three dyads were matched by unique identifier and female and male responses were compared. Results: The participants were 319 African American women and 10 white women aged 15-40 years (N = 329). Almost three fourths (72.3%) had only 1 partner over a 3-month period, compared with more than one fourth (27.7%) with ≥2 partners. Regular condom use was low (16.4%), especially with regular partners (9.1%). In the matched substudy, men reported significantly higher rates of concurrency than women (47.3% vs. 23.0%; p ≤ .002). Men who practiced concurrency were not significantly more likely than other men to use condoms with regular partners. Conclusions: Women seldom used condoms with their regular male partners and these partners had significantly higher rates of concurrency and low rates of condom use. Women may underestimate the risk of acquiring STI from regular partners. Counseling strategies should include the risk of being infected with STDs such as trichomonas by regular partners as well as by casual partners in the absence of condom use. © 2008 Jacobs Institute of Women's Health.