In the period 1997-2001, 466 sentinel lymph nodes from 342 lymphatic basins in 322 melanoma patients were examined at the Health Unit of Florence. The lymphatic mapping was performed through pre-operative lymphoscintigraphy using technetium-labelled nano-colloid, intradermal injections of vital blue dye and intra-operative gamma-probe. The examined patients were 182 females and 140 males. Sentinel lymph node was one in 65.2% of cases; two sentinel lymph nodes were detected in 27% of cases and more than 2 sentinel nodes were detected in 7.8% of cases. Melanoma metastases in one or more sentinel lymph nodes were found in 61/322 patients (18.9%). Lymphatic basins resulted to be involved by melanoma metastases were 64/342 (18.7%); sentinel lymph nodes containing metastatic melanoma deposits were 73/466 (15.6%). No metastasis was found in patients with melanoma thickness < or = 1 mm. One or more positive sentinel lymph nodes were found in 7.5% of patients with melanoma thickness > 1.00 and < or = 1.50 mm, in 27.7% of patients with melanoma > 1.50 and < or = 3.00 mm, in 38.2% of patients with melanoma > 3.00 and < or = 4.00, and in 60.7% of patients with melanoma > 4.00 mm. Frozen section analysis of sentinel lymph nodes, performed in 59/61 patients with nodal metastases, detected nodal involvement in 21 patients (35.6%). Metastases were identified by routine hematoxylin-eosin staining in 57/64 positive lymphatic basins; in 7 cases (11%) metastases were detected by immunohistochemical stainings (S100 and HMB-45). A nodal nevus was found in 3/466 sentinel lymph nodes (0.6%). Our data are analyzed and compared to previously data of the literature. The value of frozen section analysis and the major problems in the diagnosis of melanoma micrometastases in sentinel lymph nodes are discussed. The importance of the sentinel node biopsy for the detection of occult metastases and for the correct staging of melanoma patients are stressed, according to the new TNM melanoma classification.