Background: Some studies have indicated an inverse relationship between cancer risk and sunlight exposure. Others have reported that the prognosis of some cancers such as prostate, colon, ovarian and non melanoma skin cancer, were affected by the season in which the cancer was diagnosed. In our study, we evaluated whether season is prognostic in Turkish patients with breast cancer. Materials and Methods: A total of 517 patients from Kayseri Training and Research Hospital were analysed retrospectively. Patients were divided into 4 groups according to season of cancer diagnosis: winter, spring, summer and autumn. The prognostic factors for disease free survival and overall survival were investigated. Results: No significant differences were found among groups regarding prognostic factors overall. Only estrogen receptor status and lymphovascular invasion were independent prognostic factors (p=0.001 and p=0.001 respectively). We found significantly differences for mean disease free survival among groups (p=0.019). Winter group had better mean DFS while summer group had worse DFS. Mean overall survival was similar in the four groups (p=0.637). Conclusions: The season is not an independent predictive factor. However, due to interaction with other factors, we think that the season of cancer diagnosis is important for cancer prognosis.