We report two cases of idiopathic interstitial pneumonia (IIP) with acute deterioration after bronchoalveolar lavage (BAL). Case 1 was a 54-year-old woman, and case 2 was a 75-year-old man. Both were diagnosed as having IIP, and hospitalized with complaints of high fever and dyspnea. After BAL, the degree of dyspnea increased. White blood cell count and lactate dehydrogenase were elevated, and PaO2 was decreased. Chest X-ray revealed consolidation of the upper lung fields and reticulo-granular shadows spreading through both lungs. BAL fluid examination showed an elevated neutrophil fraction (case 1: 6.5%, case 2: 35.2%), suggesting respiratory tract infection although bacteria could not be detected. Case 1 died of respiratory failure despite corticosteroid therapy. Autopsy revealed diffuse alveolar damage with focal pneumonia in the right S6 corresponding to the upper lobe consolidation. Case 2 improved after antibiotic therapy. These findings suggest that aspiration of infected fluid during BAL can cause acute exacerbation of IIP. It is important to recognize that the BAL procedure can induce an acute exacerbation of IIP.