Malignant blue nevus (MBN) is a rare melanocytic lesion and controversy exists whether it is a melanoma or a unique entity. We sought to establish clinical behavior using a large national registry. All patients with MBN and melanoma from 1973 to 2008 were identified in the Surveillance Epidemiology and End Results tumor registry. We performed comparative and survival analysis among the two tumor types. A total of 228,038 patients were identified (227,986 with melanoma and 52 with MBN). The mean age was 57.7 years. Both lesions had similar age of presentation (55.8 vs 55.7 years, P = 0.527), sex (male 50 vs 55%, P = 0.44), and nodal positivity rate (9.6 vs 5.4%, P = 0.22). MBNs were more likely to be nonwhite (11.8 vs 1.6%, P < 0.0001) and present with metastatic disease (15.2 vs 4%, P = 0.0028). MBN and melanoma had a similar survival (264 vs 240 months, P = 0.78) and remained similar when stratified by race (264 vs 242 months, P = 0.99) and stage (264 vs 256 months, P = 0.83). This is the largest study to date demonstrating similar clinical behavior and survival between patients with MBN and those with melanoma. We believe MBN is a variant of melanoma and suggest using a similar treatment algorithm as that of melanoma.