We describe the clinicopathologic features of a 69-year-old man affected with acute onset Churg-Strauss syndrome with major peripheral nerve involvement. At admission the patient presented a one-week history of distal upper-limb asymmetrical paresthesias. Asthma had been present since the age of 55 and treated with leukotriene receptor antagonists (LTAs, Montelukast) for a few years. Multiple pulmonary infiltrates had been diagnosed during follow-up for melanoma. During hospitalization he showed rapidly progressive weakness worsening within a few hours; cerebrospinal fluid analysis, cervical MRI, head CT scan, nerve conduction studies and peripheral nerve and skeletal muscle biopsies were performed. Blood analysis showed leukocytosis and marked eosinophilia; p-ANCA were positive. Sural nerve biopsy showed a marked loss of myelinated fibers, thrombosed vessels surrounded by mononuclear and eosinophilic cells, necrotizing and hyaline degeneration. Eosinophilic infiltrates were shown in May-Grunwald-Giemsa stained sections. The eosinophils mostly occupied the outer zone of the adventitia at the margin of the active lesion. Perivascular cellular infiltrates within the epineurium were immunoreactive for T-lymphocytes and macrophages. Strong HLA-DR immunostaining was present in the perineurium and membrane attack complex deposition was present in a few endoneurial capillaries. Muscle biopsy showed neurogenic changes and one vessel surrounded by mononuclear cells. After a few days of corticosteroid therapy leukocytosis and eosinophilia normalized and the patient's clinical features stabilized.