We report the case of 66-year-old male, presenting with high fever since twenty days before admission, cough, progressive dyspnea, weakness and weight loss. Computed tomography of the chest showed interstitial fibrosis with distribution and morphology more suggestive of UIP pattern, compatible with the patient's clinical findings. Renal function tests and biopsy of the kidney revealed a segmental necrotizing glomerulonephritis with little or no immunoglobulin deposition (pauci-immune) on immunofluorescence. Finally our diagnosis of microscopic polyangiitis expressed as interstitial lung fi¬brosis, was confirmed by positive perinuclear antineutrophil cytoplasmic antibodies (p-ANCA). Pneumon 2006,19(1):59-64.