BACKGROUND AND OBJECTIVES: Trichomoniasis is common among sexually active women, but its importance as a cause of morbidity among sexually active men remains uncertain. STUDY DESIGN: The article outlines areas of controversy and presents pertinent new data from case-control and natural history studies. RESULTS: Trichomonas vaginalis was documented in 11% of 447 men at risk for a sexually transmitted disease. Although 54% of infected men complained of urethral discharge, the discharge was only mild or moderately severe. Elimination of Trichomonas vaginalis was associated with resolution of urethritis. CONCLUSIONS: Trichomonas vaginalis is an important consideration in sexually active men with urethral symptoms or inflammation but with little or no evidence of discharge on physical examination.