Two hundred and four patients with small breast cancer (T < or = 3.0 cm. N0 or N1a) were given breast conserving treatment (radiation group: 101, non-radiation group: 103) during the period from Feb. 1988 to Jan. 1995. Survival analysis of breast conserving treatment radiation group versus non-radiation group revealed the following: 1) Breast conserving treatment had a good prognosis, and a 5-year overall survival rate of 96.2%. 2) There was no significant difference of 5-year overall, disease-free and ipsilateral breast disease-free survival rate between the radiation group and non-radiation group. 3) Surgical margin involvement was the most significant risk factor in local recurrence after breast conserving treatment, and non-radiation was a possible risk factor. 4) Local recurrence was a significant risk factor for distant metastases after breast conserving treatment the same as node positive. These results suggested as follows: 1) Lumpectomy with a clear margin and radiation is the best choice for small breast cancer (T < or = 3.0 cm, N0 or N1a). 2) Adjuvant therapy after surgical treatment is necessary for local recurrence.