The aim of the study was to compare the frequency of Chlamydia trachomatis infection in patients with cervical intraepithelial neoplasia (CIN) and in women without cervical pathology. In a study group of 423 patients with histologically proven CIN and in 108 controls with normal cervical smear, cytological material for direct immunofluorescence analysis was obtained. Among 423 patients, 24 (5.7%) had CIN 1, 108 (25.5%) CIN 2 and 291 (68.8%) CIN 3. Among all patients with CIN, 27 (6.4%) were C. trachomatis positive and 396 (93.6%) C. trachomatis negative. In the control group 6 (5.6%) were C. trachomatis positive and 102 (94.4%) C. trachomatis negative. The difference between C. trachomatis infection incidence in patients with CIN and in women without cervical pathology was not significant (χ2=0.29; P>0.05). In this study, no difference in C. trachomatis infection incidence was detected between patients with CIN and women with normal cervical smears. The impact of C. trachomatis infection seems not to interfere with the development or even the promotion of CIN.