The present study was done to determine the influence of tumor stage and the patients' age on the number of pelvic lymph nodes obtained during standard pelvic lymphadenectomy before radical retropubic prostatectomy. Furthermore, we assessed whether the number of pelvic lymph nodes examined affects the sensitivity of pN-classification. The data of 283 consecutive patients who had undergone standardized open pelvic lymphadenectomy and radical retropubic prostatectomy for clinically organ-confined prostate cancer were reviewed retrospectively. There were striking interindividual differences in the number of lymph nodes (5-40; median: 16). The quantity was independent of pathologic tumor stage (pT) and the patients' age. In cases with 13 or more lymph nodes examined, the rate of metastatic involvement was twice as high as in lower lymph node counts. The detection of lymph node metastases--and consequently the prognostic accuracy of pN-classification--is mainly influenced by the total number of lymph nodes examined. These data suggest that at least 13 lymph nodes should be investigated to achieve optimum information.