Current staging of early prostate cancer separates patients into two groups: those with palpable and non-palpable tumors. Such staging relies on digital rectal examination in making this separation, despite the low sensitivity, low specificity, and low positive predictive value of this method. As an alternative, tumor volume may be useful for staging because of its powerful prognostic ability and its potential to be assessed clinically due to recent advances in imaging techniques such as transrectal ultrasound. In this study, we evaluate the utility of tumor volume in predicting progression of early prostate cancer based on the composite published evidence from nine pathologic studies of serially-sectioned prostates. Logistic regression revealed that tumor volume was a good positive predictor of all measures of tumor progression. There was a 10 percent probability of capsular invasion in tumors measuring about 0.5 cm3; 10 percent probability of seminal vesicle invasion in tumors measuring about 4.0 cm3; and 10 percent probability of metastases in tumors measuring about 5.0 cm3. These composite results suggest that tumor volume is a significant predictor of cancer progression. A volume-based prognostic index is proposed as an adjunct to staging for early prostate cancer.