AIM: The usefulness of interleukin 6 (IL-6) and its soluble receptor IL-6sR in the prediction of the biochemical recurrence was evaluated in patients with prostate cancer treated with radical prostatectomy. PATIENTS AND METHODS: IL-6 and sIL-6R serum levels were measured in 96 patients with prostate cancer. RESULTS: Using the log-rank test, it was evident that patients with preoperative serum levels of IL-6 higher than 1.2 pg/ml had a significantly increased probability of biochemical recurrence (p=0.031). We also observed that the Gleason score was associated with the risk of progression (p=0.033), but no relation was observed with TNM classification, PSA, % free PSA or sIL-6R. In a multivariate analysis, only IL-6 serum levels remained as a predictor of biochemical recurrence (p=0.040). CONCLUSION: The results presented here demonstrated the usefulness of IL-6 in predicting the biochemical progression of prostate cancer, pointing towards an association between inflammation and the aggressiveness of the tumor.