INTRODUCTION. Hypereosinophilic syndrome is produced by what is usually a multiple infiltration of eosinophils into tissues, and may be secondary or idiopathic, depending on whether it is related to a specific aetiology or not. It is not uncommon for it to include nerve disease, but it is unusual for it to do so in the form of multineuritis. Exceptionally, pathogenesis into multiple mononeuritis appears to be related with neurotoxicity due to products derived from eosinophils rather than with infiltrating or inflammatory phenomena. This study describes the case of a female patient with hypereosinophilic syndrome with no verifiable cause, multineuritis and eosinophilic fasciitis. CASE REPORT. A 30-year-old female with no relevant history who visited because of some painless inguinal nodules that had appeared several weeks before. At almost the same time, she presented painful sensitive symptoms in her legs with a significant functional incapacity. An important degree of hypereosinophilia, eosinophilic fasciitis and non-neoplastic eosinophilic infiltration of the bone marrow was found, together with multiple mononeuritis. Treatment with oral corticoids improved the dermatological and haematological clinical features, and associating it with gabapentin improved the neuropathic symptoms. CONCLUSIONS. The patient, in accordance with current criteria, presented idiopathic hypereosinophilic syndrome with an undetermined subtype. To our knowledge, the association with eosinophilic fasciitis and multineuritis has not been reported to date. There is no proven infiltrating mechanism in multiple mononeuritis, which corroborates the poor control of the neuropathic clinical symptoms with oral corticoid therapy. Association with gabapentin, which stabilises the axonal membrane, also backs up the neurotoxic pathogenetic hypothesis.