To determine whether there is a relationship between trichomoniasis and bacterial vaginosis (BV), cervicovaginal smears obtained from 600 women were stained with the Papanicolaou technique and examined cytologically. Thirty-six (6%) of 600 women were diagnosed as having Trichomonas vaginalis [TV(+)]. Sixteen (44.4%) of 36 TV(+) cases were observed as having BV [BV(+)]. Thirty-one of 564 TV(-) vaginal smears were also positive for BV (5.5%). There was a statistically significant correlation between trichomoniasis and bacterial vaginosis (p < 0.05). It is possible that TV might create an anaerobic environment, thereby changing the vaginal flora. This flora becomes a more suitable milieu for growing of anaerobic microorganisms. It can be postulated that TV might be the most important protozoan that contributes to the overgrowth of BV-related microorganisms.