This is the fourth report in a series that reviews the experience in the Skin and Cancer Unit, from 1955 through 1982, with the treatment of basal cell carcinomas (BCCs). It concerns 862 primary (previously untreated) BCCs irradiated by a "standardized" x-ray therapy schedule. The overall 5-year recurrence rate for these lesions, as determined by the modified life-table method, was 7.4%. This rate was not significantly different from that experienced with 211 recurrent (previously treated) BCCs with a re-recurrence rate of 9.5% (P = .552). For the primary BCCs, multivariate analysis showed that increasing BCC diameter was the only independent risk factor for high recurrence rates (P = .003). The patient's age or sex, the duration of the BCC, the anatomic site of the BCC, or time-span treated (1955-1963, 1964-1972, 1973-1982) did not significantly affect the recurrence rate. Additional analysis showed that BCCs on the head less than 10 mm in diameter had a 5-year recurrence rate of 4.4% whereas those 10 mm or greater in diameter had a rate of 9.5%. Lastly, the proportion of recurrence-free treatment sites with a good or excellent long-term cosmetic outcome after x-ray therapy (63%) was lower than previous reports in this series with curettage-electrodesiccation (91%) and surgical excision (84%). Thus, if the long-term cosmetic outcome after treatment is not an overriding concern to the patient, x-ray therapy is an effective modality for many primary and recurrent BCCs.