BACKGROUND: The Montpellier cancer institute phase II trial started in 2004 and evaluated the feasibility of intraoperative radiotherapy (IORT) technique given as a sole radiation treatment for patients with an excellent prognostic and very low recurrence risk. METHODS: Forty-two patients were included between 2004 and 2007. Inclusion criteria were patients >= 65 years old, T0-T1, N0, ductal invasive unifocal carcinoma, free-margin > 2 mm. IORT was delivered using dedicated linear accelerator. One fraction of 21 Gy was prescribed and specified at the 90% isodose using electrons. In vivo dosimetry was performed for all patients. Primary end-point was the quality index. Secondary endpoints were quality of life, local recurrences, cosmetic results, specific and overall survival. RESULTS: At inclusion, median age was 72 years (range, 66--80). Median tumor diameter was 10 mm. All patients received the total prescribed dose. No acute grade 3 toxicities were observed. Late cosmetic results were good at 5 years despite the poor agreement of accuracy assessment between patients and physicians. Four patients (9.5%) experienced a local failure and underwent salvage mastectomy. The 5 year-disease free survival is 92.7% (range 79.1-97.6). All patients are still alive with a median follow-up of 72 months (range 66--74). CONCLUSION: Our results confirm with a long-term follow-up that exclusive partial breast IORT is feasible for early-breast cancer in selected patients. IORT provides good late cosmetics results and should be considered as a safe and very comfortable "one-step" treatment procedure. Nevertheless, patient assessments are essential for long-term quality results.