The aim of the study was to evaluate the importance of young age with regard to local control in a prospective cohort of 1085 women with pathological T1 tumours treated with breast conservative treatment (BCT). Patients were divided into two age groups: 40 years or younger, 7.8%, and older than 40 years, 92.2%. With a median follow-up of 71 months, the local recurrence rate was 10.6% in women < or =40 years, and 3.7% in older women. The local recurrence-free survival (LRFS) was significantly different for the two age groups, respectively 89%, < or =40 years, and 97.6%, >40 years (P=0.0046). A separate analysis showed a significantly decreased LRFS for young women with a positive family history, 75.4% versus 98.4% 5-year LRFS for older women. A worse LRFS for young women with a negative lymph node status was also observed, respectively 84% versus 98% 5-year LRFS (both P<0.001). In a multivariate analysis, taking into account the pre-treatment and treatment factors, age < or =40 years, was the only significant predictor of a decreased LRFS. Thus, young age is an important factor in relation to local control. In a subset analysis, this significant adverse effect of young age on outcome appears to be limited to the node-negative patients and those with a positive family history. To date, there is no evidence that young women with pT1 breast cancer, treated by mastectomy have an improved outcome when compared with those treated with conservative surgery and radiotherapy. Taking into account results from a subset analysis suggests that giving systemic therapy to a subgroup of women who are < or =40 years, node-negative and/or have a positive family history might give a better local control.