PURPOSE: The aim of this study was to evaluate the usefulness of sentinel lymph node (SLN) biopsy in the treatment of primary melanoma. METHODS: Fifty-one cases that were diagnosed as malignant melanoma of the skin without clinical evidence of regional lymph node metastasis and underwent SLN biopsy at Samsung Medical Center were analyzed retrospectively. A lymphoscintigraphy with peritumoral injection of radionuclide was performed preoperatively. SLNs were identified using a hand-held gamma probe and by methylene blue dye injection intraoperatively. RESULTS: Twenty patients (39%) had metastasis in the SLN and they underwent immediate complete radical dissection of the nodal basin. Among the 20 patients who had SLN metastasis, additional metastatic lymph nodes were detected in 5 patients after the complete lymph node dissection. When several clinico-pathologic parameters such as gender, age, primary tumor location, draining nodal basin, tumor depth and size of tumor were compared between SLN positive group and negative group, there was a significant difference in the mean thickness of melanoma between SLN (+) group (5+/-2.9 mm) and SLN (-) group (4.5+/-5.0 mm) (P<0.05). In the same way, as the thickness of melanoma increased, positive SLN were detected more frequently (P<0.05). Recurrences occurred in 18 patients (35.3%) during the follow-up period, but only one case in 31 patients with negative SLN recurred at the SLN basin without evidence of distant or loco-regional recurrence (false negative rate 4.8%). Lymphedema of extremity developed in 9 patients who underwent complete radical lymph node dissection and 2 patients who underwent only SLN biopsy had a very mild-form lymphedema. CONCLUSION: SLN biopsy in the treatment of cutaneous melanoma is a safe, useful and feasible method to identify status of regional lymph node with low false negative rates and low complications.