With more vigilant screening for prostate cancer, there has been an associated increase in patients with little or no residual cancer at radical prostatectomy after an initial diagnosis of minute cancer on needle biopsy. This raises a critical question as to whether the biopsy and subsequent radical prostatectomy in these patients are from the same patient. We used PCR-based microsatellite marker analysis to perform identity test in 46 men (35 with minute cancer and 11 with no residual cancer). Of them, 41 were interpretable, including 31 with minute cancer and 10 with no residual cancer. All 31 interpretable cases with minute cancer showed match between the initial biopsy and radical prostatectomy specimens. Nine of the 10 interpretable cases with no residual cancer showed match and 1 showed mismatch. The remaining 5 cases (4 with minute cancer and 1 with no residual cancer) were considered uninterpretable due to technical problems. The initial biopsy of the mismatched case had high-grade cancer (Gleason score 4 + 4 = 8) measuring 9.6 mm in length with perineural invasion. Our results confirm that, in most cases of "vanishing cancer" in radical prostatectomy specimens, it reflects a chance sampling of a minute cancer and not a switch in specimens. However, specimen switch can rarely occur, and if there is high grade or a lot of cancer on the biopsy with no or very minimal cancer in the radical prostatectomy specimen, one should evaluate for patient identity.