The natural course ofChlamydia trachomatis infection and its risk factors were studied in Colombian women with normal cytological results, during a 5-year period.Eighty-two women who were found to be positive for C. trachomatis at the start of the study were studied at 6-month intervals.At each visit, a cervical scrape sample was obtained for detection of C. trachomatis by use of C. trachomatis endogenous-plasmid polymerase chain reaction (PCR)-enzyme immunoassay and VD2-PCR-reverse line blot assay.Of the women studied, 67% had a single-serovar infection, 10% had a mixed-serovar infection, and 23% had an infection with an unidentified type.An inversed rate of clearance of C. trachomatis infection was observed with oral contraceptive use (hazard ratio [HR], 1.7 [95% confidence interval {CI}, 1.1-2.7])and first sexual intercourse at у20 years of age (HR, 4.3 [95% CI, 2.3-8.0]).Serovars of group B (B, D, and E) and C (H, I, J, and K) had a decreased rate of clearance (rate ratio, 0.4 [95% CI, 0.1-0.9]),compared with that for serovars of the intermediate group (F and G).At 4 years of follow-up, 94% of the women had cleared their infections.Chlamydia trachomatis is an obligate, intracellular, nonmotile, gram-negative bacterium recognized as one of the most common sexually transmitted agents in the world.Approximately 70% of infections with C. trachomatis run an asymptomatic course that remains undetected and can result in severe complications, such as pelvic inflammatory disease, tubal infertility (6%-21% of Chlamydia-infected women), pelvic pain (18%-24% of Chlamydia-infected women), and ectopic pregnancy (7%-9% of those who become pregnant) [1,2].In addition, an epidemiological association between the