An electron microscopical study of two consecutive nerve biopsies from a patient with metachromatic leucodystrophy (sulphatide lipidosis) was made. The ultrastructural changes observed consisted of: a) irregular whorls of myelin. The myelin in the whorls showed a thickened, sometimes doubled, intraperiod line, which was barely visible in compact myelin; b) “inclusion bodies” up to 1 μ in diameter in the cytoplasm of Schwann cells. These had a lamellar structure, with stacked membranes 60 Å apart; c) a “loose” pattern of the myelin in some nerve fibers, with loss of the intraperiod line, and d) presence of abnormally dense mitochondria with thickened cristae in Schwann cells. It is suggested that: a) the whorl formation and the ultrastructural abnormalities of the myelin in the whorls may be due to impaired myelin synthesis, and b) that the “inclusion bodies” may represent the accumulation of cerebroside sulfate in micellar aggregates. The “loose” pattern of myelin is considered artifactural until proven otherwise.