We describe an unusual family with a fatal genetic syndrome of neonatal diabetes mellitus (DM), enteropathy, endocrinopathy, and severe infections with variable thrombocytopenia. All affected individuals are male; X-linked inheritance is likely. The most common clinical features are neonatal DM, inanition, and enteropathy; a variety of other autoimmune phenomena are less frequent. Clinical variability within and among families is common, including lack of one or more cardinal features. The syndrome is usually fatal, but survival is sometimes possible with immunosuppressive therapy. Clinical variability and frequent new mutations may contribute to poor recognition and underreporting of similar cases.