The late side-effects of the local therapy of early breast cancer depend on many patient- and therapy-related parameters. We aimed at investigating the factors that influence the cosmetic and functional outcomes among our breast cancer patients after breast-conserving surgery and conformal radiotherapy, with or without adjuvant systemic therapy. A study was made of the association of the cosmetic outcome after a median follow-up time of 2.4 years and the clinical data on 198 patients extracted from a prospectively compiled database. Breast tenderness occurred more frequently among patients ≤50 years old (p < 0.05). Long-term side effects were related to radiotherapy-related factors the most, while no effect of the systemic therapy could be detected. The risk of hyperpigmentation, breast edema and breast fibrosis increased by 18%, 23% and 7%, respectively for every 100 cm(3) increase in the irradiated breast volume, while that of breast edema and breast fibrosis increased by 21% and 12%, respectively for every 10 cm(3) increase in the boost volume. Patients who received a photon boost were significantly more likely to develop breast edema and fibrosis than those who received electrons (p < 0.005). Dose inhomogeneity was related to the volume of the irradiated breast (p = 0.037). Dyspigmentation developed more often among patients older than 50 years, while smoking favoured both dyspigmentation and teleangiectasia. Breast edema was related to dyspigmentation (p = 0.003), fibrosis (p < 0.001) and breast asymmetry (p = 0.032), whereas none of these abnormalities were associated with teleangiectasia. Body image changes were more frequent at a younger age (p < 0.005), while the need to change clothing habits occurred more often at an older age (p < 0.05). Radiotherapy-related parameters appear to exert the greatest effect on the overall cosmetic outcome after breast-conserving surgery and postoperative radiotherapy.