Objective: The prostate specific antigen is used in the diagnosis of prostate diseases. In Peru, there are no studies that suggest a cut-off point of PSA index to discriminate between benign prostatic hyperplasia and prostate cancer as indicator for prostate biopsy. Based on international studies different cut-off points are used. Material and methods: A diagnostic test was performed to determine the validity of PSA index to discriminate between these two entities in patients with a total PSA between 4.0 ng/ml and 9.9 ng/ml. All 356 patients included were diagnosed of benign prostatic hyperplasia or prostate cancer by prostate biopsy. The sensitivity, specificity, predictive values and likelihood ratios of PSA index cut-off points from 25% to 15% were evaluated. The ROC curve was drawn. Results: A PSA index cut-off point of 17% has better values of sensitivity (87.8%), specificity (62.2%) and predictive values (positive predictive value of 62.4% and negative predictive value of 87.4%) compared to others to decrease the number of negative biopsies. The positive likelihood ratio was 2.3 and the negative 0.1. The area under the curve was 0.75 [IC 95%, 0.71 to 0.79]. Conclusion: We suggest a PSA index of 17% as cut-off point to discriminate between benign prostatic hyperplasia and prostate cancerin the urology outpatient consult of patients with a total PSA between 4.0 ng/ml and 9.9 ng/ml. We recommend this value as it could reduce the number of negative biopsies.