Chlamydia trachomatis infections can produce serious consequences in the women during the pregnancy and in the new born passing through the birth canal. The above mentioned, which in Venezuela studies is rare, has motivated us to carry out the present work to determine the frequency of cervical infection due to Chlamydia trachomatis in pregnant women with obstetrical complications, as to determine its relationship with the clinical epidemiological characteristic of such patients. Sixty endocervical swabs from pregnant women with complications who assisted to the Obstetric Emergency Service at the Autonomous University Hospital (AUH) were analysed from april to octuber 2000. For detecting Chlamydia trachomatis direct fluorescent antibody staining (bioMERIEUX) was used following the factory recommended methodology. Of the 60 analysed samples, 8 (13.33%) were positive for C. trachomatis. Seventy five percent with diagnosis of threat of premature birth followed by threat of premature birth + premature rupture of membranes complications (25%). No relationship between cervical infections by C. trachomatis and the clinical epidemiological characteristics were found in the patients. However, infection by C trachomatis was seen more frequently in women in low socioeconomic conditions, low educational level, and whose sexual relations were iniciated at an early age.