Cervical and endometrial samples from 33 women with lower genital tract infection (LGTI) or pelvic inflammatory disease (PID) were evaluated for Chlamydia trachomatis major outer membrane protein gene (omp1) polymorphism. Polymorphism was correlated with symptoms, clinical findings, and histopathology. F, E, I, D, H, K, and G genotypes were represented. Thirty-seven genotyped samples (66%) displayed omp1 mutations compared with prototype sequences. Significantly, 7 of 7 women with variant F infections had PID compared with 6 non-variant F infections in women with LGTI (P = .003). PID was defined by clinical findings or plasma cells on endometrial biopsy. Of interest, F variants were associated with histopathology. Eleven women (92%) with E genotypes were asymptomatic. Our data suggest that F variants are associated with symptomatic, severe endometrial disease, whereas E genotypes are associated with asymptomatic, milder infections. Detection of virulent genotypes may provide a prognostic indicator for serious sequelae. Larger studies are required to evaluate the molecular, immunologic, and epidemiologic basis for these findings.