Churg-Strauss syndrome is part of the spectrum of systemic vasculitis, but can be distinguished from the other necrotising vasculitides on the basis of clinical and histological criteria. Renal involvement is not regarded as a prominent feature and is generally mild. We report a series of 19 patients with Churg-Strauss syndrome referred to the Hammersmith Hospital between 1976 and 1986. Renal involvement was common (84%) and often severe: three patients had nephrotic syndrome; four presented with serum creatinine greater than 500 mumol/l; and two required dialysis. Focal segmental glomerulonephritis was the predominant lesion on biopsy (85%), often with necrotising features and crescent formation. Extravascular granulomata and eosinophilic infiltrates were uncommon. Treatment with high-dose prednisolone was generally successful in milder cases, but was not always sufficient to halt the progression of more severe vasculitis. In these cases, additional immunosuppressive therapy with azathioprine, cyclophosphamide or plasma exchange was of benefit. Renal disease improved in 14 of 16 patients, ten of whom have maintained normal renal function on follow-up. Only one patient died, as a result of progressive cardiac disease.