In order to more effectively monitor women with dysplasia of the uterine cervix, a dysplasia clinic was established at the University Women's Hospital, Basel, in 1970. From 1970 to 1978, 3,570 women were examined in the clinic. The mean age of the patients was 36.4 +/- 13.3 years. Since in most cases we administer therapy to women whose cervical smear reports indicate at least severe dysplasia, we devoted our attention to those patients with smears showing mild-to-moderate dysplasia. Of the 2,528 women who had such smears, 111 were not followed up in our clinic. Mild-to-moderate dysplasia was demonstrated only once in 1,110 patients and was found at least twice in 1,051 women. Progression to a cervical smear showing at least severe dysplasia occurred in 256 patients (10%). This progression, however, was demonstrated in 87% of the 256 patients as early as the first two years of monitoring. Our observations make it clear that strict surveillance of patients with dysplasia even in the mild or moderate stage is necessary. With strict monitoring, the anticipated progression in 10% of the patients can be detected early; as a result, we can achieve successful secondary prophylaxis of cervical carcinoma.