Cervical cytology screening was performed, between July 1971 and the end of 1976, on 503,870 specimens from 226,428 women. During this period the rate of positive or suspicious findings fell from 2.6% to 0.9%. The number of specimens judged suspicious for invasive carcinoma, carcinoma in situ or with severe dysplasia (among those women who had undergone serial examinations) was 5 per thousand for the first specimen, 2 per thousand for a subsequent second specimen, and 1.6 per thousand for a subsequent third specimen. The screening programme detected (later confirmed histologically) 272 cases of invasive carcinoma and 948 of carcinoma in situ or severe dysplasia. Related to the number of women screended at various ages, the frequency of carcinoma in situ and severe dysplasia had a peak between the 25th and 29th year of life, with a second, lower peak at around the 65th year. For invasive cervical carcinoma the frequency remained high into old age. The proportion of histologically proven cases of invasive carcinoma fell continuously from 1963/66, at 3.6 per thousand, until 1976, at 1.6 per thousand.