Introduction: Presence of multimorbidity can affect prognosis, treatment, and outcomes of individuals with cancer. However, the prevalence and factors associated with multimorbidity among older late-stage melanoma is not well studied. We estimated the prevalence of any type of pre-existing multimorbidity (autoimmune disorder (AD), physical health conditions (PHC), and mental health conditions (MHC)) among older adults with late-stage melanoma in the United States. We further examined the association of patient-level factors to multimorbidity in late-stage melanoma. Methods: We derived data on older fee-for-service Medicare beneficiaries (age ≥ 66 years) diagnosed with late-stage melanoma between 2011 and 2015 (N = 4,519) from the linked Surveillance, Epidemiology, and End Results cancer registry and Medicare claims. We defined multimorbidity as the prevalence of two or more chronic conditions prior to the diagnosis of melanoma. We used unadjusted and adjusted logistic regressions to examine the association of patient-level factors to multimorbidity. Results: An overwhelming majority (85%) of older patients with late-stage melanoma had multimorbidity. Pre-existing PHC multimorbidity (84%) was the most prevalent, followed by AD (12%), and MHC (6%). Age and region were associated with any and PHC multimorbidity. Sex, marital status, and region were factors associated with pre-existing AD while sex, marital status, and dual eligibility were associated with MHC multimorbidity. Conclusions: Pre-existing multimorbidity was highly prevalent among older individuals with late-stage melanoma; prevalence rates and factors associated with multimorbidity varied by type of chronic conditions. This highlights the need for developing systematic approaches to optimizing care of older patients with late-stage melanoma and multimorbidity.