Adherence to Mediterranean diet has been consistently associated with a reduced mortality in the general population, but evidence for women with breast cancer is scanty. METHODS: A cohort of 1453 women with breast cancer diagnosed between 1991 and 1994 in northern Italy was followed-up for vital status for 15 years after diagnosis. The pre-diagnostic habitual diet was assessed through a structured questionnaire and adherence to the Mediterranean diet was evaluated through the Mediterranean Diet Score. Hazard ratios (HR) of death with confidence intervals (CI) were estimated using Cox model, adjusting for potential confounders. RESULTS: Compared to women who scarcely adhere to the Mediterranean diet (n = 332, 22.8%), those highly adherent (n = 500, 34.4%) reported higher intakes of carbohydrates, mono-unsaturated and poly-unsaturated fatty acids, vitamins, folate, and carotenoids, and lower intakes of cholesterol and animal proteins. Adherence to the Mediterranean diet was associated with a better prognosis: 15-year overall survival of 63.1% for high and 53.6% for low adherence, respectively (p = 0.013). HR for all-cause mortality was 0.72 (95% CI: 0.57-0.92) and HR for breast cancer mortality was 0.65 (95% CI: 0.43-0.98) for women 55 years and older. No significant association emerged for breast cancer mortality in the total cohort. CONCLUSIONS: Although dietary habits may have changed after breast cancer diagnosis, these findings indicate that women who ate according to the Mediterranean dietary pattern prior to their diagnosis may have greater chance of a favorable prognosis after breast cancer diagnosis compared to those who did not.