['Lymph lymph node metastasis from melanoma ≤0.50 mm (ultrathin) is an infrequent event. However, because many newly diagnosed melanomas are ultrathin, a significant proportion of patients who present with lymph node disease have an ultrathin melanoma. The authors hypothesized that ultrathin melanomas that present with lymph node metastasis represent biologically aggressive lesions with a worse prognosis.', 'The Surveillance, Epidemiology, and End Results registry data were queried to identify patients with cutaneous melanoma who presented with lymph node metastasis diagnosed between 1998 and 2008. Hazard ratios (HRs) from Cox proportional hazards regression models were used to compare disease-specific survival (DSS) between various tumor depths.', 'In total, 6134 patients with lymph node-positive melanoma were identified and stratified according to tumor depth, including 588 (10%) with a tumor depth ≤0.50 mm, 519 (8%) with a tumor depth from 0.51 to 1.00 mm, 1669 (27%) with a tumor depth from 1.01 to 2.00 mm, 1871 (31%) with a tumor depth from 2.01 to 4.00 mm, and 1487 (24%) with a tumor depth >4.00 mm; and the respective 5-year DSS rates were 63%, 76%, 75%, 60%, and 43%. Multivariable analysis confirmed a similar trend in HRs for DSS: The HR was 1.00 for a tumor depth ≤0.50 mm (reference category) and 0.64 (P < .001), 0.65 (P < .001), 0.95 (P = .57), and 1.42 (P < .001) for tumor depths of 0.51 to 1.00 mm, 1.01 to 2.00 mm, 2.01 to 4.00 mm, and >4.00 mm, respectively. This association of tumor depth with DSS persisted for N1 and N2 disease but not for N3 disease.'] Is ultrathin primary a marker for worse prognosis in lymph node-positive cutaneous melanoma?