AIM: To assess the value of intraoperative diagnostic examination of frozen sections of lymph nodes removed during radical prostatectomy. METHODS: Pelvic lymph nodes from patients with prostatic carcinoma were obtained (1) as frozen sections during radical prostatectomy, to exclude patients from non-curative surgery, and (2) as paraffin sections postoperatively from lymphadenectomy performed at radical prostatectomy, to stage the tumour and assess need for adjuvant treatment. Findings from the two approaches were used to assess the accuracy and cost of frozen section diagnosis, and to judge the results of omitting intraoperative diagnosis. RESULTS: In 82 patients frozen section revealed metastasis in six (7.3%), and metastases were found in a further four (4.9%) on paraffin sections (false negatives). Of the 195 patients undergoing staging lymphadenectomy (without frozen section), metastatic cancer was seen in nine cases (4.6%). The frozen section cost of metastatic cancer detection per patient was calculated as 7516 Pounds (550 Pounds x 82/6), with an associated false negative rate of 33%. CONCLUSIONS: Frozen section diagnosis of metastatic carcinoma in pelvic lymph nodes before radical prostatectomy has a high false negative rate and is costly. It may not be justified with the observed low incidence of lymph node metastasis.