A study was made to compare the incidence, quality and aetiology of complications after low and high dose-rate intracavitary radiotherapy for St. Ia-IIb cervical carcinoma in 185 patients, of whom 84 were treated with radium (R) and 101 with afterloaded Co60 (Cathetron, C), from 1969 to 1976. The frequency of surgery and external irradiation was similar in both groups. There were more (p=O.Ol) complications in group C (27.7 %) than in group R (13.1 %). However, when the single fractions in the Cathetron treatment were lowered from 10 Gy to 7.5 Gy each in 1972, the incidence of complications decreased from 42.4 % to 20.6 % (p=0.02) and the latter incidence was not statistically different from group R. Intestinal complications were more frequent than urological ones in both groups. Low weight was significantly (p<0.025) correlated with the development of complications and previous laparotomy (p=O.OOOl) with the development offistulae in group C.