Chronic interstitial pneumonia (PIC) are rare in infants. We report a case of an infant who presented with a chronic interstitial pneumonia following an infection with a respiratory syncytial virus. The diagnosis was confirmed histologically (open lung biopsy). The failure of oral steroid therapy (Prednisolone 2 mg/kg/day) led to the use of boluses of methylprednisone (30 mg/kg/day, daily for three days in three series one month apart). The treatment led to a progressive improvement and thirty months after the last bolus the respiratory examination was normal as was the radiology. The efficacy of bolus steroid therapy observed by other authors should be confirmed in multicentre trials using surgical biopsy to precise the pulmonary lesions.