A 35-year-old woman at 28 weeks' gestation presented with purpura, arthralgia and proteinuria. After a skin biopsy had suggested necrotizing vasculitis, prednisolone was administered. Renal biopsy following delivery disclosed crescents in about 60% of glomeruli. After stopping prednisolone, purpuric lesions and arthralgia reappeared. A second renal biopsy demonstrated cellular crescents in about 80% of glomeruli. The symptoms disappeared on restarting prednisolone. However, the patient progressed to renal failure in 8 months. Histological examinations of the kidney and skin suggested microscopic PN.