The results are reported of a study on the psychological side-effects of mass screening for cervical cancer in Rotterdam. The reactions of participants towards a positive smear and towards the treatment which followed the positive smear were analysed. Women who had problems with a positive smear and with a serious disorder which necessitated an operation and hospitalization had problems with the treatment. However, most women who underwent the operation did not have lasting problems of either a psychological or somatic nature. Women who had been treated by their G.P.s or by a gynaecologist in most cases did not have problems with their treatment. The final conclusion was that mass screening for cervical cancer in Rotterdam caused psychological side-effects to occur among women with a positive smear. However, for the majority of women with a positive smear they were not of a lasting or serious nature.