TAFRO syndrome is a rare variant of idiopathic multicentric Castleman's disease, for which disseminated non-tuberculous mycobacteria (NTM) infection must be excluded. However, due to the slow and fastidious growth of the organisms, identification of the pathogen is often challenging. We herein describe a case of disseminated Mycobacterium genavence infection, in which manifestations of the patient were confusingly similar to those of TAFRO syndrome. A 69-year-old Japanese man presented with prolonged fever accompanying pain in his back and ribs on the right side. Systemic investigations revealed thrombocytopenia, marked elevation of alkaline phosphatase, anasarca (pleural effusion and ascites), megakaryocytosis in the bone marrow, and hepatomegaly. Magnetic resonance imaging (MRI) showed diffuse, T1-and T2-low-intensity spotted lesions on his vertebral bodies, but biopsy showed inconclusive results. The patient met the diagnostic criteria of TAFRO syndrome and was started on prednisolone, which improved his general condition shortly thereafter. Blood culture after 42 days of incubation revealed the presence of Mycobacterium; however, we considered it a contamination at that time because no organisms grew on conventional agars, and the patient was discharged. Ten weeks after the isolation of Mycobacterium, he developed persistent fever and was readmitted. This time, vertebral bone mallow biopsy demonstrated a large amount of mycobacterium, which was later successfully identified as M. genavense by sequencing analysis. Under a final diagnosis of disseminated M. genavense infection, we treated the patient with clarithromycin, rifampicin, and ethambutol. This case highlighted that disseminated NTM infection may follow a similar clinical course as that of TAFRO syndrome.