Mortality was studied in 18,357 patients (33% males and 67% females) with skin hemangioma admitted to Radiumhemmet between 1920 and 1959. The treatments of the hemangiomas were performed by radium-226 sources (13,094 patients) or x-ray therapy (2,540 patients). In 2,723 patients no radiotherapy was given. The median age was 6 months for the treated patients and 8 months for the patients not receiving radiotherapy. Between 1920 and 1951 a total of 154 patients were reported dead. The cohort was matched with the Swedish Cause of Death Register between 1952 and 1985. During that period 504 died, in 146 patients the cause of death was cancer or leukemia. The total number of person-years at risk was 587,426. In patients treated with radium-226 or orthovoltage x-rays, 410 deaths occurred (standardized mortality ratio (SMR) = 1.07; ns). In patients given contact therapy 34 deaths occurred (SMR = 0.82; ns) and in the not irradiated group 60 deaths occurred (SMR = 0.78; ns). Patients treated with radium-226 or orthovoltage x-rays had an SMR of 1.34 for all cancers combined (p less than 0.05). For patients treated between 1920 and 1939 the SMR for cancer was 1.53 (p less than 0.05) as compared to an SMR of 1.16 (ns) for those treated between 1940 and 1959.