Familial hemophagocytic lymphohistiocytosis is a very unusual cause for demyelination and the clinician would do well to be aware of the condition, especially when children present with atypical findings on magnetic resonance imaging associated with fever, pancytopenia, and hepatosplenomegaly. This is a rare autosomal recessive, multisystem inflammatory disorder characterized by widespread organ infiltration by macrophages and activated lymphocytes. It is usually diagnosed in the first 2 years of life and is rapidly fatal if untreated. Reported here is the case of a 12-year-old boy, from a poor family, with a 6-year history of visual loss and fever for 5 months, and transient hemiparesis with hepatosplenomegaly and pancytopenia. Cranial magnetic resonance imaging showed multiple areas of hyperintense signal, predominantly involving white matter. The boy also had elevated triglycerides and ferritin, with low fibrinogen level. Bone marrow aspiration revealed hemophagocytosis. He was diagnosed as having familial hemophagocytic lymphohistiocytosis and treated with the HLH 2004 protocol. A sibling also had evidence of hemophagocytosis. Remission was achieved, but his parents could not afford the cost of hematopoietic stem cell transplantation. He relapsed after 8 months and later died.