Horizontal gaze palsy associated with progressive scoliosis (HGPS) is a rare autosomal recessive condition that has been recently mapped to a 30-cM region on chromosome 11q23-25. In this report, we describe a consanguineous family in which three of five sibs are affected with HGPS. In two of the affected sibs, there was significant cognitive delay in addition to congenital horizontal gaze palsy and childhood onset scoliosis. In all three affected sibs, magnetic resonance imaging (MRI) scans revealed brainstem hypoplasia, a finding that has recently been associated with HGPS. Clinical examination of the family showed no significant dysmorphic features, while karyotyping, EMG, nerve conduction, and muscle biopsies were unrevealing. Homozygosity mapping was performed to narrow the disease locus on 11q23-25. A recombination event was observed in one affected sib between markers D11S1345 and D11S4464, which further refined the region to a 9-cM interval. Since the MRI results provide support for the theory that maldevelopment of neurons in the abducens nuclei and caudal longitudinal fascicle is the cause for HGPS, we speculate on the existence of a gene in this 9-cM interval on chromosome 11q23, which is critical for brainstem development.