In a randomised trial, the cosmetic results after sector resection and axillary dissection with or without postoperative radiotherapy for early breast cancer were evaluated. The evaluations were made at 3, 12, 24 and 36 months (357, 326, 302 and 255 women, respectively) after treatment. Good to excellent cosmetic results were achieved in 84-90% of those in the group randomised to radiation and in 91-95% in the group allocated to surgery only, as judged by the women themselves, and in 81-86% and 87-93%, respectively, according to other observers. At 12 months the results in 290 patients were photographically documented and evaluated by a panel. The results were good to excellent in 35-84% of the irradiated group and in 62-93% of the non-irradiated group. Poor results followed the development of contour differences, breast oedema and mamillary deviation, which were the most important mediators of a poor cosmetic result after radiotherapy. We conclude that sector resection and axillary dissection can be performed with good cosmetic results. Doses to 54 Gy of radiotherapy influence the result negatively, but from a clinical standpoint to a moderate extent.