Three members of a family with normal parents had a common constellation of findings that included absent corpus callosum and recurrent bacterial infections. The older male and female siblings both died from infection at an early age. The patient’s CBC was significant for elevated numbers of monocytes that were large and vacuolated. Her T- and B-cell function was normal. These preliminary findings suggested a defect in innate immunity. Evaluation of the patient’s peripheral blood monocytes by flow cytometry showed normal size and maturity. Phagocytosis and activation of peripheral blood derived macrophages by cytokines were also similar to controls. In contrast, the patient’s cultured macrophages were significantly more spread than those from normal individuals and contained a disordered actin cytoskeleton when cultured on fibronectin. The ability of the macrophage to transmigrate across an endothelial cell barrier was impaired. However examination by time-lapse videomicroscopy showed that the mutant macrophages had increased protrusional activity and movement. This is the first report describing a genetic macrophage motility disorder that results in an increased susceptibility to infection.