Age at first coitus and use of oral contraceptives were studied in a highly homogeneous population (French Canadian) during a cytologic cervical cancer screening program. Both factors were known in 84,540 women without cervical lesions and in 2017 patients with mild and moderate dysplasia. Highly significant correlations were found between: early onset of sexual activity and occurrence of dysplasia; oral contraceptive use and occurrence of dysplasia; early age at first coitus and oral contraceptive use. When correlated for age at first coitus, there was a significant excess of dysplasias in oral contraceptive users. Dysplasia of the uterine cervix behaves epidemiologically like carcinoma in situ and invasive squamous carcinoma, that is, essentially as a venereal disease. It remains to be seen whether all dysplasias form one continuum or whether there are two morphologically similar but biologically distinct forms of dysplasia: one more frequent, regressing spontaneously, the other relatively rare, progressing to carcinoma in situ and invasive squamous carcinoma of the cervix.