OBJECTIVE Radioisotope guided sentinel lymph node (SLN) dissection (SLND) for prostate cancer has been shown to increase the sensitivity of detecting early metastases in open pelvic lymph node dissection. We developed a technique that allows SLND to be performed by laparoscopy in conjunction with laparoscopic radical prostatectomy. METHODS In 71 consecutive patients SLND was performed by 1 surgeon preceding laparoscopic radical prostatectomy. Mean preoperative prostate specific antigen was 8.88 ng/ml (range 2.1 to 25.4). At 24 hours prior to surgery 3 ml (200 MBq) Tc labeled human albumin colloid were injected into the prostate gland under transrectal ultrasound guidance. An especially designed laparoscopic gamma probe was used to measure radioactivity during surgery. SLNs were identified and removed. If frozen section analysis showed metastases, extended pelvic lymph node dissection was performed. RESULTS Radioactivity was detected on 2, 1 and no sides in 50 (70.4%), 19 (26.7%) and 2 patients (2.8%), respectively. In 81 of the 142 pelvic side walls (54.7%) SLNs were exclusively outside of the obturator fossa. Histopathological examination showed metastases to SLNs in 9 patients (12.9%). Eight of the 11 detected metastases (72.7%) were outside of the obturator fossa. Lymph node metastases were exclusively found in Tc marked lymph nodes. Mean tumor size was 1.7 mm (range 0.2 to 3.9). CONCLUSIONS SLND is feasible by laparoscopy. It detects micrometastases outside of the obturator fossa in a significant number of patients. We noted that the transperitoneal approach allowing wide exposure and a gamma probe with a 90-degree lateral energy window is the most important factor to enable successful laparoscopic SLND.