This study is the largest series of Trichomonas infection in men diagnosed by urine cytology in the literature. Most men had no prior diagnosis of trichomoniasis and received specific antibiotic therapy based on their urine cytology results. Urine cytology may represent the initial diagnostic test for Trichomonas in men, and accurate cytologic diagnosis may prevent undesired adverse outcomes for them and their partners. Cancer Cytopathol 2017;125:55-59. © 2016 American Cancer Society.