Trichomonas vaginalis is is a monoxenous parasite which lives in human urogenital systems and causes sex transmitted disease through human sexual contact. Disease frequency has been seen at different rates in different communities or in the same community depending on people's sociocultural status. Previously we made a study for determining prevalence of T. vaginalis infection in woman living in Istanbul. We made this present study for determining any difference in prevalence in comparison to the results of ten years earlier. A total number of 207 vaginal discharge samples which were collected from two different hospitals, (93 from Venereal Diseases Hospital [VDH] and 114 from Cerrahpasa Ob&Gyn Clinic), were evaluated under direct microscopy and were cultured for T. vaginalis in a Cystein-Peptone-Liver-Maltose (CPLM) medium. T. vaginalis was observed under direct microscopy and grew in culture in 2 (0.97%) of 207 vaginal discharge samples [1 (1.1%) patient from VDH and 1 (0.9%) patient from Cerrahpasa]. The incidence of trichomoniasis has significantly decreased compared to the year 2000 in both VDH and Cerrahpasa populations (p=0.038) according to X2 test results. This epidemiologic study shows the importance of social development in the incidence of infectious diseases.