Microscopy and culture iare classical methods used to detect T. vaginalis. However, both culture and microscopy rank below polymerase chain reaction (PCR) assay in analytical sensitivity. The paper describes a study to measure the concentration of T. vaginalis in biological samples and, by using the pre-established values of the analytical sensitivity of microscopy and culture, to determine their diagnostic sensitivity that is equal to 42.9 and 60.5%, respectively. In this connection, the proportion of patients with the Trichomonas infection diagnosis unestablished by these methods was at least 57.1% for microscopy and 39.5% for culture.