We assessed the association between obesity measurements including visceral adipose tissue (VAT), measured by computed tomography, and the risk of high-grade prostate cancer after radical prostatectomy. We investigated 296 patients who were diagnosed with prostate cancer and underwent radical prostatectomy. Data extracted from medical records included age, body mass index (BMI), VAT, pretreatment prostate-specific antigen (PSA) levels and Gleason score (GS). We performed logistic regression to examine the association between indicators of obesity and a higher GS (⩾4+3). Among the 296 patients, 107 (36%) had a higher GS. After controlling for age and PSA, BMI was not associated with GS (odds ratio, OR=1.039, 95% confidence interval, CI=0.943-1.145; P=0.437). BMI had different effects on GS depending on VAT. When the data were stratified by the median VAT value, a higher BMI was significantly associated with a higher GS in patients with VAT⩾130.5 cm2 (OR=1.218, 95% CI=1.028-1.443; P=0.022), but not in those with VAT<130.5 cm2 (OR=0.912, 95% CI=0.783-1.062; P=0.236). A higher BMI was associated with an increased risk of high-grade cancer only in patients with more VAT.