OBJECTIVE Evaluation of results of breast conserving therapy in early stage breast cancer and of importance of time interval between surgery and radiotherapy. METHODS Descriptive study. METHODS Free University Hospital, Amsterdam. METHODS In the period 1980-1989, 554 patients with 560 invasive breast cancers were referred for radiotherapy after wide local excision of the tumour with axillary lymph node dissection. The dose to the breast was 50 Gy + 15 Gy boost dose. In case of positive margins, a higher boost dose (20-25 Gy) was given. Node-positive patients received adjuvant chemotherapy (premenopausal patients) or hormonal therapy (postmenopausal patients). RESULTS The median follow-up period was 82 months (range 52-160 months). The 5 and 10-year survival rates were 86.7% and 72.6%, respectively. Local (breast) relapse occurred in 22 patients (3.9%). The breast recurrence rate was 8/329 (2.4%) for patients who started radiotherapy within 7 weeks after surgery, as against 14/231 (6.1%) for patients with a longer interval (p < 0.05). In Cox's proportional hazards analysis, age (negative relation), T-stage and interval between surgery and radiotherapy were identified as independent factors predictive of breast recurrence (p < 0.05). CONCLUSIONS A delay of radiotherapy after breast conserving surgery of more than 7 weeks can adversely affect the local tumour control rate.