We report a retrospective study of diabetic children, 0--14 years of age, from seven Swedish departments of paediatrics. There were 359 new cases in the years 1970--1975. Notification suggested that there was a mean yearly incidence of 19.6 cases per 100 000 with a year to year variation of 10.0--26.4 per 100 000. Consequently about 330 new cases of childhood diabetes would be expected in Sweden every year. Incidence varied considerably between different geographical areas. The age distribution was bimodal with a main peak at about 12 years and another peak at about 7 years. There was some evidence for clustering of new cases in January and the autumn. The mean prevalence of childhood diabetes in the seven districts was 1.3 per 1 000.