Eosinophilia, brawny induration, and tenderness of the skin and deeper tissues, and eosinophilic and lymphocytic infiltration of skin, deep fascia, and muscle characterize the acute eosinophilia-myalgia syndrome associated with ingestion of L-tryptophan. Many patients have a florid inflammatory myopathy. We evaluated 10 patients with this syndrome in whom peripheral neuropathy was a prominent or the only presenting feature. Two of these patients with severe neuromuscular disease required mechanical ventilation, and 1 died. Clinical severity appeared to be positively associated with the total dose of L-tryptophan ingested. Although the inflammation is generally thought to be more severe in skin, fascia, and muscle, inflammation, especially in the epineurium of sural nerve, was sometimes striking and often accompanied by vasculopathy and angioneogenesis. These cases draw attention to a new preventable syndrome with peripheral nerve involvement, emphasize the value of tissue biopsy for its diagnosis, and raise issues related to pathogenesis.