Triple-negative breast cancer (TNBC) (ER-/PGR-/erb-2-) constitutes an aggressive subtype in breast cancer because it is accompanied by a significant decrease in overall survival (OAS) and recurrence-free survival (RFS) compared with hormone receptor positive breast cancers. This retrospective cohort study investigates the following issues: (1) Is there an impact of guideline-adherent treatment on RFS and OAS in TNBC? (2) Which adjuvant treatment has the most important impact on RFS and OAS in TNBC? This German retrospective multi-centre cohort study included 3,658 patients with primary breast cancer recruited from 2000 to 2005. The definition of guideline adherence was based on the German national S3 guideline for diagnosis and treatment of breast cancer (2004). A total of 371 patients (10.1%) had TNBC. Compared with HR+/erb-2- breast cancer (P = 0.001; HR = 1.75; 95% CI: 1.27-2.40), the recurrence rate of TNBC was significantly higher (P < 0.001; HR = 2.86; 95% CI: 2.17-3.76). Furthermore, the 5-year RFS and OAS was significantly lower in TNBC (RFS: 74.8% [95% CI: 68.8-80.8%] vs. 86.5% [95% CI: 84.6-88.4%] [log-rank P = 0.0001]) (OAS: 75.8% [95% CI: 69.9-81.8%] vs. 86.0% [95% CI: 84.1-87.9%] [log-rank P = 0.0001]). The most important parameters predicting RFS and OAS in TNBC after receiving guideline-conform chemotherapy are guideline-adherent surgery, radiotherapy, nodal status and grading. Overall, 66.8% TNBC were found with one or more (18%) guideline violations, which subsequently impaired OAS and RFS. The most important impact on OAS and RFS in TNBC patients was because of guideline violations (GV) concerning adjuvant radiotherapy and GV concerning adjuvant chemotherapy. Patients with TNBC primarily have a worse prognosis in terms of RFS and OAS than patients of a primarily non-TNBC phenotype. There is a strong association between guideline-adherent adjuvant treatment and improved survival outcome in TNBC. The outcome significantly decreases with the number of guideline violations.