BACKGROUND: Peripheral and tissue eosinophilia are associated with a group of idiopathic inflammatory syndromes. The idiopathic hypereosinophilic syndrome represents a spectrum of disorders characterized by prolonged eosinophilia of an undetectable cause and significant organ dysfunction. The pathogenic role of the eosinophil in these conditions is attested to by evidence of eosinophil activation and degranulation at sites of tissue injury. Recently, an overlapping range of idiopathic eosinophilic muscle disease with an overall good prognosis has been described. RESULTS: We describe a patient with a syndrome of idiopathic myositis with eosinophilia and eosinophilic cellulitislike cutaneous manifestations. Histopathological studies of the skin and muscle revealed eosinophilic infiltration. Elevated serum levels of eosinophilic cationic protein and interleukin-5 paralleling disease activity were detected. CONCLUSIONS: This patient demonstrates clinical and laboratory features of eosinophilic myositis with eosinophilic cellulitislike skin lesions. The elevated serum levels of interleukin-5 and eosinophilic cationic protein may be responsible for the eosinophilia and tissue injury, respectively. With the advances in our understanding of cytokine-dependent regulatory mechanisms governing the eosinophil reaction, more targeted ways of manipulating eosinophilia as well as the entry and activation of eosinophils within specific tissues can be expected.