Some investigators consider small-volume prostate cancer (0.5 ml or less) without Gleason pattern 4/5 elements as clinically insignificant. The objective of this study was to characterize the anatomic distribution and pathologic features of small tumors (aggregate volume of 0.5 ml or less) in whole-mount prostatectomy specimens. Between 1999 and 2003, 371 consecutive patients underwent radical prostatectomy at the Indiana University Hospitals for localized prostate cancer. Patients who received hormonal or radiation therapy prior to the surgery were excluded from the study. A total of 62 specimens with total tumor volume of 0.5 ml or less were identified and included in this study. All specimens were embedded and whole-mounted. Tumor volume was measured using the grid method. The mean age at the time of surgery was 59 years (median, 61 years; range, 37-72 years). The mean preoperative prostate-specific antigen (PSA) was 6.5 ng/ml (range: 0.3-18 ng/ml). The mean prostate weight was 53 g (range: 16-132 g). The mean tumor volume was 0.29 ml (median, 0.35 ml; range, 0.02-0.48 ml). Tumor multifocality and bilaterality were present in 69 and 37% of cases, respectively. Three (5%) had positive surgical margins. The largest tumor was located in the peripheral zone, transitional zone, and central zone in 79, 16, and 5% of cases, respectively. The largest tumor was located in the anterior prostate in 10 cases (16%) and in the posterior prostate in 52 cases (84%). The distribution of Gleason scores was 5 (12 cases, 19 %), 6 (40 cases, 65 %), and 7 (10 cases, 16 %). One case had a primary Gleason pattern 4. None had extraprostatic extension, seminal vesicle invasion, or lymph node metastasis. Small-volume prostate cancers are often multifocal and bilateral, with predilection for the peripheral zone. Of these small-volume cases, 16% had Gleason pattern 4 and might, therefore, be clinically significant.