Chlamydia trachomatis infections are the most prevalent bacterial sexually transmitted infections (STI) recognized throughout the world. The aim of this study was to determine the prevalence of Chlamydia trachomatis among a randomized statistical group of women suffering from cervicitis in Tehran- Iran . During a 12- month- period, Jan 2003 to Jan 2004, 142 endocervical samples were taken from women suffering from cervicitis attending to Mirzakoochakkhan Women Hospital in Tehran , Iran . Direct fluorescent antibody (DFA) and PCR techniques were used to detect Chlamydia trachomatis in endocervical samples. Twenty two (15.5%) [95% CI, 9.54-21.4] of 142 samples were diagnosed as Chlamydia positive according to PCR results, while DFA diagnosed 20 (14.1%) positive cases [95% CI, 8.37-19.8]. No statistically significant difference was found between two diagnosis methods applied in this study. The prevalence was the highest (25%) among women aged 25 to 29 yr and 35 to 39 yr. The x ² test showed a significant relationship between positive test result and bearing a history of STI (P= 0). The results of this study showed high prevalence of C. trachomatis infection among women suffering from cervicitis and suggested that patients diagnosed with genital Chlamydia infection should be referred to the genitourinary medicine clinic for further STI screening and partner notification.