Between 1928 and 1986, 393 keloid sites on 250 patients were presented. Three hundred seventy-five sites received superficial quality therapeutic irradiation. Etiologies were determined. The majority were excised prior to irradiation, and in these, histologic confirmation was obtained. Recurrence rate after irradiation was low, 9/375 (2.4%). When 7 of 9 recurrences are eliminated for post-irradiation ear lobe repiercing, true recurrence is only 2/375 (0.53%). Cosmetic result was considered excellent without recurrence in 92%; favorably improved with hypertrophic scar, nodule or altered pigment in 5.6%; and marginally improved with smaller, less symptomatic keloid in 2.4%. Significant complications were limited to persistent pigment disturbance in only 1 patient, and pre-irradiation hemorrhage in 1 patient (unrelated to radiotherapy). There was no wound dehiscence nor failure to heal irradiated incision site. Transient hyperpigmentation occurred in 91/375 (24%). Recurrence after irradiation was too rare to associate with etiology, specific technical factors, keloid configuration or velocity of initiating the post-operative radiotherapy. An unexpected finding was that 22/250 (9%) were Caucasian subjects. Our null (0%) carcinogenicity rate to date and the one-half of one percent true recurrence rate supports continued use of post-operative irradiation to prevent keloid formation in this group of documented troublesome keloid formers. Configuration subtypes are proposed, post-operative irradiation protocol is listed, and mechanism of action is explained in accordance with the dynamic pathophysiology of keloid.