To determine the risk associated with previous herpes simplex type-2 (HSV-2) infection and possibly other virus infections, a prospective study of cervical neoplasia in more than 10,000 women was performed in the 1975-1983 period. The subjects were selected at random from an alphabetical listing of eligible women living in one district of Prague. At enrollment colposcopy and cervical cytology were performed, a blood sample was taken and data regarding education, socio-economic status, personal habits and sexual and reproduction-associated attributes were obtained from each woman. A total of 10,683 women were enrolled; a complete set of data was obtained in 10,389 women. Women with normal or non-significant findings were invited for further colposcopical and cytological investigations after 2 years and 4 years, the other women were followed at 3- to 6-monthly intervals. In women with highly significant findings, histological investigation was performed. The total of 150 cases of moderate to severe dysplasia (i.e. cervical intraepithelial neoplasia, grade II, CIN II), 83 cases of carcinoma in situ (CIN III) and 21 cases of invasive carcinoma (INCA) were detected. More than 60% of the patients were ill at enrollment, the other cases developed in subjects with originally slightly suspicious (27 CIN II, 17 CIN III, 3 INCA) or negative findings (30 CIN II, 12 CIN III, 3 INCA). Analysis of the data indicated significantly positive correlation of one or more of these clinical conditions with a number of sexual and reproduction-related attributes of which early age at first intercourse was most consistent. Among the other attributes, the smoking habit was associated with the highest risk of developing the disease. A negative correlation of cervical neoplasia with several attributes was demonstrated; of these diathermoelectrocoagulation of the ectopic epithelium and transformation zone of cervix was the most important single protective factor. On the basis of these findings, control subjects were selected for serological studies.