Inclusion body myositis is characterized by an insidious onset, progressive indolent course, and is generally felt to be refractory to standard therapy for myositis. We reviewed the charts of 32 patients with muscle biopsy findings suggestive of inclusion body myositis. The average time from symptom onset to diagnosis was 37 months, but initially 40% were incorrectly diagnosed. Twenty-eight patients (88%) were classified as definite or probable inclusion body myositis and were treated with various combinations of prednisone and immunosuppressive agents. Sixty-eight percent of those treated experienced a decrement in function and muscle strength. Three patients exhibited longterm improvement while 12 patients experienced delayed progression, defined by short term improvement in strength or a stable functional class, All of these patients received therapy, 5 in the form of methotrexate and prednisone. All untreated patients deteriorated clinically. In summary, (1) inclusion body myositis is a clinically distinct entity which is frequently misdiagnosed initially. (2) While clinical improvement with therapy is rare, our observations support recent reports that therapy may be associated with a slower rate of clinical progression. (3) Optimal therapy remains uncertain, but the use of low dose methotrexate and prednisone may warrant further study.