The technique for obtaining a cytological cervical smear using Papanicolaou's stain ("Pap smear") is an established screening procedure. Discussion centres on the ideal intervals for smear test repetition and the age groups to be included in screening programmes. The effective interval and age breakdown were therefore studied in the patient population seen by us at the University Gynaecology Clinic in Basel. It was found that predominantly younger women took part in screening programmes. Fifty percent of the women had two smear tests within 18 months. It was also found that the interval between smear tests increased as patients grew older. With the recommendation of an annual smear test, screening in Basel covers 37% of women in one year and 76% in three years. Results in private patients are more favourable. In the light of these data, an annual smear test should continue to be recommended in all circumstances.