We attempt to clarify the impact of the learning curve on the first 30 laparoscopic pelvic lymphadenectomies performed at our institute. Open surgical revision of the area of laparoscopic dissection was performed at radical retropubic prostatectomy. The mean number of obturator and iliac lymph nodes removed laparoscopically was 8.7 and 8.8 from the right and left sides, respectively. The mean number of residual obturator and iliac lymph nodes removed at open operation was 3.2 and 3 from the right and left sides, respectively. The amount of residual lymph node tissue after laparoscopic lymphadenectomy progressively decreased with time, especially after the first 20 cases. A microscopic pelvic lymph node metastasis was found at open operation in patients 6, 14 and 15, who had false-negative results at laparoscopy. Due to the learning curve effect, the first 30 patients who undergo laparoscopic pelvic lymphadenectomy should be assessed again by an open operation at radical retropubic prostatectomy.