Identification and histologic study of the sentinel node (SN) is an acceptable, yet not firmly established, guide for treating intermediate-thickness melanoma. This study widens the range of applications of this technique. We included 97 patients with intermediate-thickness melanoma lesions or lesions for which there is no standard treatment. Fifty-six underwent preoperative lymphoscintigraphy, and all underwent intraoperative lymphatic mapping (IOLM) using blue dye, followed by frozen section study and total node processing by serial sections. Elective lymph node dissection was performed in cases of metastasis to the sentinel node or technical failures with high risk. Four categories were defined: (A) intermediate-thickness lesions (mean 2.27 mm) (n = 45); (B) thin lesions (mean 1.14 mm) with risk factors of regional failure (n = 27); (C) lesion thickness close to but more than 4 mm (n = 10); and (D) lesions of undetermined thickness (n = 15). Median follow-up was 30 months (range 13-51 months). Intraoperative lymphatic mapping successfully identified the sentinel node (SN) in 93% of basins explored. Metastases were detected in 11 SNs. There were three lymph basin recurrences in patients with previously negative SNs, all salvaged by therapeutic lymph basin dissection and are NED (no evidence of disease). Two SN(+) patients had systemic recurrences; one died of his disease, and the other is alive with disease. One SN(-) patient died NED owing to other cause. This technique spared 83% of category A patients from lymph node dissection. It allowed better staging and better decision making for treatment in categories B and D; and it prevented early regional recurrences in category C patients. Intraoperative lymphatic mapping with SN guidance is a novel, lo