OBJECTIVE: Bacterial vaginosis (BV) is associated with significant morbidity. Bacterial vaginosis is due to an overgrowth of anaerobic organisms in the vagina. It has been postulated that the presence of Trichomonas creates an anaerobic environment that favors BV. Thus, BV should be more frequent in the presence of Trichomonas if Trichomonas is creating a favorable anaerobic environment. MATERIALS AND METHODS: A retrospective review of Pap test reports was performed for a diagnosis of coccobacilli consistent with shift in vaginal flora, that is, the presence of clue cells. Cases were Pap smears with Trichomonas identified. Controls were cases without Trichomonas. Results were analyzed using Fisher exact test. RESULTS: Four hundred cases were reviewed; 200 with and 200 without Trichomonas. The incidence of BV was significantly higher in the Trichomonas group (46.5%) than in group without Trichomonas (24.5%) (p < .0001.). CONCLUSION: The presence of Trichomonas on a Pap smear is associated with an increased incidence of BV. The report of Trichomonas on a Pap smear should prompt clinical consideration that BV may be present.