In this study, we tested the hypothesis whether breast conserving therapy (BCT) compared with mastectomy is associated with a negative outcome in terms of distant metastases or death (DMD) and investigated the relation between locoregional recurrence (LRR) and DMD in young breast cancer (BC) patients. This study included a consecutive series of 536 patients ≤40 years of age at diagnosis with pathological T1N0-3M0 BC, treated between 1989 and 2005. A multistate survival model was used to evaluate the influences of local treatment and LRR on DMD, adjusted for potential prognostic factors. Patients were treated with mastectomy (N = 213) or BCT (N = 323). Median age at diagnosis was 36.3 years, with a median follow-up of 9.0 years. The 10-year actuarial cumulative incidence of DMD was 30.6 % after mastectomy and 26.3 % after BCT (P = 0.04). In total, 81 (15 %) LRRs were observed. After BCT, patients had a threefold higher risk of LRR than after mastectomy (HR 2.9; 95 % CI 1.6-5.3). Patients with LRR had a higher risk of DMD compared with patients without LRR (HR 5.5; 95 % CI 2.1-14.5). However, BCT was not negatively associated with DMD-after-LRR (HR 0.47; 95 % CI 0.2-1.1, BCT vs mastectomy). In conclusion, although LRR significantly affected DMD, the increased risk of LRR after BCT compared with mastectomy did not lead to a worse DMD outcome in BC patients ≤40 years of age.