It has been demonstrated that breast surgery may induce prolactin (PRL) increase. Because of the potential stimulatory role of PRL on breast cancer cells, its postoperative increase may influence the prognosis of breast cancer patients. This study was performed to evaluate the influence of surgery-induced hyperprolactinemia on recurrence rate in operable breast cancer. The study included 250 consecutive breast cancer patients, clinical stage T1-3 N0-2M0, who were observed for a median follow-up of 72 months. Surgery-induced hyperprolactinemia occurred in 108/250 patients (43%). Irrespectively of node involvement, hormonal receptor, type of surgery and adjuvant therapies, the relapse rate was significantly higher in patients who had no surgery-induced hyperprolactinemia than in those with postoperative PRL increase (64/142 vs. 23/108; p < 0.001). This difference was also significant in relation to node status (N0:22/63 vs. 5/56, p < 0.001; N+:42/79 vs. 18/52, p < 0.05). The present study shows that a surgery-induced rise of PRL, despite its potential stimulation of cancer cell growth, is paradoxically associated with a longer disease-free survival in operable breast carcinoma in both patients with or without axillary node involvement. Moreover, this study suggests that the prognosis of node-negative patients who did not show postoperative hyperprolactinemia tends to be similar to that of patients with node involvement and surgery-induced PRL enhancement. Therefore, the lack of surgery-induced hyperprolactinemia would have to be grouped together with the unfavorable prognostic factors of breast cancer.