The number of cases of intraepithelial carcinoma of the cervix among women of different age groups has been related to the number of cervical smears from women of the same age groups. Among women aged 25 to 34 years the incidence of intraepithelial carcinoma was 0·67% and among those aged 35 to 44 years it was 0·75%. The overall rate of intraepithelial carcinoma in women under 35 years was 0·55% compared with an overall rate of 0·59% in women over 35 years. If screening of women for cervical cancer is to play any part in preventive medicine it is suggested that the national campaign for the early detection of cervical cancer should be expanded to encourage practitioners to take cervical smears from younger women, particularly from those under 35 years.