Hymenoptera stings may be responsible for both local and systemic reactions; these can be immediate or delayed, depending on the time between the sting and the development of signs or symptoms. Delayed clinical reactions have been reported, although unusual, due to serum sickness and/or affecting organs or systems generally not involved in the immediate reaction, such as heart, kidneys, central and peripheral nervous systems. This paper describes the clinical and immunological findings in a 51-year-old subject, who, after two stings of paper wasps, the second one after the third venom immunotherapy (VIT) injection, presented immediate large local and systemic allergic reactions which quickly improved after e.v. methylprednisolone administration. About 40 hours later, he developed acute polyradiculoneuropathy with muscle weakness, paresthesia, difficulties in standing up and walking. Skin tests and specific IgE determination showed allergy to paper wasp. The activation, by wasp venom, of peripheral blood mononuclear cells in primary culture, evaluated by tritiated thymidine incorporation proliferation assay, showed an important hypersensitivity to wasp venom. Therefore our results suggest the hypothesis that the polyradiculoneuritis causative etiopathogenetic mechanism might be a delayed immunological response to wasp antigens followed by an allergy-triggered autoimmune reaction, as previously suggested by other authors; they found lymphocytic infiltrates in demyelinization areas and at perivascular levels, by histologic examination of autoptical and bioptical material of patients with nervous system lesions after hymenoptera stings.