A 79-year-old female presented with weight loss and vomiting. Physical examination was normal other than cachexia. A disseminated malignancy was suspected. A positron emission tomography/computed tomography (PET/CT) scan showed extensive fluorodeoxyglucose uptake in enlarged lymph nodes and lesions in the lung, liver, bone, brain, and breast. Thrombocytopenia and a leucoerythroblastic blood film suggested bone marrow infiltration. The bone marrow aspirate showed infiltration by nonhematopoietic cells (panels A and B; original magnification ×10 and ×40, respectively). The cells were large with an eccentric nuclei and abundant, pale cytoplasm with vacuoles. The trephine biopsy (panel C; original magnification ×40) was infiltrated by pleomorphic cells arranged in loose, discohesive sheets containing a moderate amount of cytoplasm and prominent nucleoli. There was no visible melanin pigment. The clinical history and PET/CT pointed to either a disseminated lymphoma or epithelial malignancy. However, immunohistochemistry for CD45, lymphoid markers, and pancytokeratin was negative. Further immunohistochemistry revealed that the cells were positive for CD117, S100p, HMB45, and Melan A (panel D; original magnification ×40). Hence, a diagnosis of amelanotic melanoma was made. No skin lesion was identified. The patient deteriorated and died 2 weeks after diagnosis.Melanoma affecting the bone marrow is rare. In the absence of an obvious skin lesion and the lack of melanin pigment, the diagnosis can easily be overlooked.