Familial amyloidotic polyneuropathy type I is an autosomal dominant inherited disorder characterized by progressive peripheral and autonomic neuropathy, associated with neural and systemic amyloid deposits. The abnormality usually lies in the transthyretin (TTR) gene. We report a 25 years old man with 18 months history of dysesthesias and pain in the toes, abnormal micturition and sexual dysfunction. Neurophysiologically studies disclosed a sensory-motor axonal polyneuropathy. Autonomic tests showed sympathetic and parasympathetic involvement. An electron micrograph of sural nerve revealed amyloid fibrils in the endoneurium. His mother died after a clinical history suggestive, in retrospect, of familial amyloidotic polyneuropathy type I. The clinical and genetic analysis of this cause of polyneuropathy are discussed (Rev Méd Chile 2003; 131: 1179-82).