AbstractWe report a family with five of six siblings (including identical male twins) with a novel constellation of immunologic and neurologic impairments. Affected subjects experienced severe dermatitis starting around 9 months of age, Stevens–Johnson syndrome in early childhood, and extreme elevations of IgE (9,400–43,000 IU/ml). The oldest sibling died at age 27 of respiratory failure following recurrent, severe pneumonias. All four surviving affected siblings have had chronic sinusitis or otitis, cutaneous vasculitis, and recurrent bacterial pneumonias leading to bronchiectasis. Neurologic features in all five siblings included oral motor deficits, dysarthria, low average IQ (70–80), and essential myoclonus. Four had documented ataxia and/or mild sensory loss with increased patellar but diminished ankle reflexes. The nonconsanguineous parents and one sibling had none of the above findings, consistent with autosomal recessive inheritance. This primary immunodeficiency with distinctive neurological impairments represents a new syndrome. Published 2003 Wiley‐Liss, Inc.