The incidence of malignant tumours of different types during pregnancy was studied. Special attention was paid to the presence and treatment of preinvasive and invasive carcinoma of the cervix uteri. The series consisted of 100 malignancies of different types in pregnant patients treated at Departments I and II of Obstetrics and Gynaecology, University Central Hospital, Helsinki, during 1950–69. The total number of pregnant patients admitted during this period was 153 424 and the incidence was thus 0.07%. In 65 cases interruption of pregnancy was the sole intervention as the patient had been or was treated elsewhere. Of these cases, 63 were extragenital malignancies and two were carcinoma in situ of the cervix. The material included another 13 cases of carcinoma in situ of the cervix, making an over‐rule incidence of 0.009%. Invasive carcinoma of the cervix was diagnosed in 17 patients. They were all treated at this clinic. The incidence was 0.01%. Over 5 years have elapsed from the treatment of 9 patients. Eight of these 9 patients were alive after 5 years, but one died after 7 years. The patients treated less than 5 years ago are alive and asymptomatic. In addition, four other malignant tumours of the genital tract and one mediastinal neurinoma that had metastasised into the abdominal cavity were diagnosed.