Background: It is unknown whether all thick melanomas share the same prognostic features. We present a large, multi-institutional study on thick melanoma, evaluating for factors prognostic of survival. Methods: We queried the database of the Sentinel Lymph Node Working Group for patients with thick melanoma (>4 mm) who had a sentinel lymph node biopsy from 1993 to 2018. Clinicopathologic characteristics were correlated with overall survival. Results: There were 1,235 patients with a median follow-up of 28 months. Median thickness was 5.9 mm, with 713, 356, and 166 cases having a thickness of >4 to 6, >6 to 10, and >10 mm, respectively. Ulceration was seen in 51.2% of cases, while sentinel lymph node metastases were seen in 439 of 1,235 (35.5%) cases. For melanomas >4 to 6 mm, age, thickness, ulceration, lymphovascular invasion, and sentinel lymph node metastasis were correlated with overall survival (all P < .05), but for melanomas >6 to 10 mm, only sex and sentinel lymph node metastasis were prognostic of overall survival (both P < .05). For melanomas >10 mm, only sentinel lymph node metastasis predicted overall survival on multivariable analyses (P < .05). Conclusion: Prognostic markers of overall survival for thick melanoma include thickness, ulceration, and sentinel lymph node metastasis, but also include other unique factors such as lymphovascular invasion. Moreover, certain prognostic markers for survival are associated with different subgroups of thick melanoma, which vary based on thickness group.