To determine whether serum follicle-stimulating hormone (FSH) can be used to predict the aggressiveness of prostate cancer prior to radical prostatectomy. Methods: Ninety-six patients who underwent radical prostatectomy for biopsy proved cT1c-T2N0M0 prostate cancer between 2003 and 2008 were identified for retrospective analysis. Using univariate regression analysis, potential variables of extraprostatic tumor extension were identified, including prostate-specific antigen (PSA), luteinizing hormone, FSH, testosterone, biopsy findings, and age. These variables of interest were analyzed by logistic and linear regression analysis to determine if serum FSH is predictive of extraprostatic extension. Results: Extraprostatic extension was pathologically confirmed in 18 of 96 patients (18.8%). Statistical analysis confirmed that serum FSH was significantly associated with extraprostatic extension (P=0.04). However, age, PSA level, Gleason score, number of tumors, and serum testosterone level were not found to be independent predictors of extraprostatic extension. Conclusions: Selective expression of FSH receptor on the surface of blood vessels of prostate cancers has recently been reported. Measuring serum FSH preoperatively in patients with prostate cancer may provide clinically relevant information about extraprostatic spread of tumor.