The authors report the brain findings in six cases of familial erythrophagocytic lymphohistiocytosis (FEL) and review the literature, focusing primarily on the neurologic and neuropathologic aspects. Clinically, the most common neurologic abnormalities in the six patients were stupor or coma and seizures, with hemiplegia and cranial nerve palsies. Neuropathologic changes were characterized by infiltration of the meninges by lymphocytes and histiocytes and perivascular lymphocytic cuffing and diffuse proliferation of histiocytes in the brain parenchyma. The severity of the brain involvement was variable. In the mildest case there was only meningeal involvement. More severely involved cases showed meningeal and perivascular infiltration of lymphoid cells in the brain. In the most severely involved cases, there was, in addition, diffuse cerebral infiltration by histiocytes accompanied by multifocal necrosis. Some cases showed disproportionately greater involvement of the brain than of the visceral organs. The authors conclude that "meningoencephalitis," histiocytic invasion, and necrotizing brain lesions are characteristic of FEL, although the mechanism of their production is not known. Frequent seizures and disseminated intravascular coagulopathy may be contributory.