OBJECTIVE To investigate the morbidity and pathological features of incidental prostate cancer and their clinical significance. METHODS 1483 prostate specimens obtained during operation, including transurethral resection of prostate (TURP) and total resection of the prostate, for the diagnoses of benign prostatic hypertrophy (BPH) or bladder cancer between January 1999 and August 2005 underwent pathological examination and 34beta12 and p63 immunohistochemical staining so as to detect incidental prostate cancer. The volume of incidental prostate cancer was calculated by the image analysis system. The clinical data were analyzed retrospectively. Comparison between the clinical and pathological feature of incidental prostate cancer was made. RESULTS 53 cases of incidental prostate cancer, with the Gleason scores from 2 (1+1) to 9 (4+5) and the volumes from 0.18 to 1440.00 mm(3) were detected. The morbidity of incidental prostate cancer was 3.6%. The volume of 47 cases (88.7%) were less than 0.5 cm(3) as the threshold of insignificant cancer, and the volumes of 6 cases (11.3%) were more than 0.5 cm(3). All incidental prostate cancers of clinical significance were detected in the TURP samples. Among the incidental prostate cancers found in the TURP samples 20% were clinically significant cancers. The clinically significant incidental cancers were located in the central or transitional zone with the Gleason scores of 3 + 4 (2 cases), 4 + 2 (1 case), or 4 + 5 (3 cases). These clinically significant cancers were of diffuse distribution, and their preoperative clinical features were negative in palpation/image examination, elevation of serum PSA, and negative in puncture examination. CONCLUSIONS Nowadays, the morbidity of incidental prostate cancer is lower than that of 1980s'. Among the incidental cancers 11.3% were of clinical significance. That the preoperative clinical examination cannot find these clinical significant cancers is partially caused by the pathological features of these tumors.