An analysis was made of 51 Chinese patients who tested positive for antimyeloperoxidase antibody (anti-MPO) in the five-year period from 1989 to 1993 in Hong Kong. Nineteen could be clearly classified as having an identifiable vasculitic illness, while the features of the remainder were suggestive of vasculitic syndromes in most cases. Renal disease was present in 84% of all cases and was the commonest manifestation, followed by pulmonary diseases. Acute or acute-on-chronic renal failure developed in 20 patients (39%). Of those who had renal biopsy performed, over half had histologic evidence of crescentic glomerulonephritis. Anti-MPO associated disease carried a grave prognosis with significant morbidity and mortality. Steroid and immunosuppressive therapy was given to most of the patients and in those who responded to immunosuppressive therapy, anti-MPO was a useful marker for monitoring disease activity. Twenty patients died, either of complications or as a result of disease activity.