The objective is to evaluate the prognostic value of preoperative magnetic resonance imaging (MRI) findings in breast cancer patients aged less than 40 years. This retrospective, single-center study evaluated 92 women aged <40 years who received a diagnosis of invasive breast carcinoma between 2008 and 2012. These patients underwent a breast MRI before treatment and follow-up at the same institution. Kaplan-Meier survival curves were used to analyze overall survival, with the log-rank test used to compare different groups. Cox regression analysis was used to estimate hazard ratios (HRs) with 95% confidence interval (95% CI) values. The mean age of the patients was 34 years (range: 25-39 years) and the mean tumor size was 3.9 cm in maximal dimension (range: 0.7-10.5 cm). Recurrence was observed in 21 (22.8%) patients and 15 (16.3%) patients did not survive during a mean follow-up period of 5.4 ± 1.9 years. MRI findings associated with worse overall survival included tumor size >5 cm (HR:5.404; 95% CI:1.922-15.198; p = 0.017), presence of non-mass enhancement (HR:3.730; 95% CI:1.274-10.922; p = 0.016) and multifocal tumor (HR:3.618; 95% CI:1.151-11.369; p = 0.028). Inconclusion, MRI findings that are suggestive of more extensive disease were associated with worse overall survival in young breast cancer patients.