C. trachomatis is an important cause of sexually transmitted diseases, being mainly associated to cervicitis or urethritis among female and male patients, respectively. This study was designed to evaluate the frecuency of C. trachomatis infection among female patients attending a bith control facility using chlamydia IgG and IgM antibody detection, and to correlate this findings with the presence of C. trachomatis at the endocervix. Two hundred fertile women attending a hostital associated birth control facitity were evaluated by indirect microimmunofluorescence (IMIF) to detect circulating antibodies and with direct microimmunofluorescence (DMIF) to detect C. trachomatis in endocervix. C. trachomatis was present in 24 percent (44/200) of endocervical samples. IgG antibodies were equally prevalent in both DMIF positive group had higher antibody titers than the negative group (54,1 vs 32,9 percent, p < 0,05). Moreover, the DMIF positive group was associated with a higher frecuency of chlamydia IgM antibodies than the DMIF negative group. (97,5 vs 4,6 percent, p < 0,0001). These results indicate that C. trachomatis is a frequent agent of infection among women asking to be included in a birth control programm and also suggest that epidemiological surveillance studies are needed