BACKGROUND Synchronous detection of multiple myeloma and acute myeloid leukemia in a single patient is a rare coincidence. Treatment of these patients is still unclear, mostly based on acute myeloid leukemia strategies combined with bortezomib. METHODS A 72-year-old male with no medical history was investigated for pancytopenia. On medical examination, he was complicated with a wide and severe skin infection on arm. On examination of bone marrow aspirate, 25% myeloblasts infiltration and additional 10% plasma cells were seen. Acute myeloid leukemia was diagnosed and plasma cell proliferation was attributed to reactive plasmacytosis due to skin infection. However, flowcytometric studies and immunohistochemical examination revealed two different cell populations with 30-40% atypical plasma cells and >20% myeloblasts. Serum M-protein detected by serum electrophoresis test and immunofixation test revealed a monoclonal IgG lambda band. He was diagnosed with concurrent acute myeloid leukemia and multiple myeloma without history of chemotherapy.Management and outcome: The patient was initially treated with bortezomib and dexamethasone for the myeloma. Subsequently, azacitidine was administered subcutaneously for the acute myeloid leukemia treatment. The tru-cut biopsy of the lesion on his arm revealed suppurative inflammatory findings and no malign cells detected. Antibiotherapy was started according to susceptibility. He expired after three months of survival. CONCLUSIONS The synchronous occurrence of these two different clonal hematological malignancies is rare in hematology practice. Patient-based prospective studies and case series are needed to guide diagnosis and treatment strategies. Furthermore, this report highlights the importance of ruling out reactive plasmacytosis in patients with hematological malignancy who developed severe infections.