This experiment identified intelligence-related gait characteristics in unobstructed level-walking and when negotiating obstacles and stairs. Sixteen subjects with mental retardation (WAIS-R Full-Scale IQ range 50-73, Mean=60.3) were age and gender matched with 9 female and 7 male nonretarded subjects. Unobstructed level-walking for the subjects with mental retardation was characterised by higher cadence and, for females, shorter strides than the nonretarded controls. In stepping over and across obstacles, the subjects with mental retardation crossed the obstacle earlier in their stride and stepped over obstacles with greater clearance. The females with mental retardation crossed the obstacle very early in the lead-foot stride and correspondingly late for the trail foot. In stair ascent, the relative duration of the step cycle phases were reliably different for the individuals with mental retardation. Since information-processing explanations for the data were not entirely adequate, it is suggested that deficiencies in the visual discrimination of moving displays by individuals with mental retardation might account for these findings.PsycINFO classification: 2221; 2300; 2330; 3256.