Achondroplasia is a relatively frequent genetic disorder that may lead to limb weakness, motor-mental retardation, hydrocephaly, and respiratory disorders. In this pathology, foramen magnum stenosis and accompanying disorders like respiratory depression is well documented.A 2.5 year-old child with the diagnosis of achondroplasia admitted to our clinic with severe respiratory depression, limb weakness, and motor mental retardation as well as sympathetic dysfunction. In radiologic evaluations, severe foramen magnum stenosis was detected. The patient was operated and posterior fossa decompression was accomplished to prevent compression of respiratory centers and neurons.This case is unique with the narrowest foramen magnum reported up to date and the sympathetic dysfunction which is not reported as a complication in achondroplasic patients. The authors review the relevant literature, focusing on the indications for cervicomedullary decompression in infants with achondroplasia.