Aim: Postinfectious bronchiolitis obliterans (PIBO) is an infrequent yet potentially severe disorder following acute lower pulmonary infection (ALRI) in children. In infants and young children PIBO have been strongly associated with Adenovirus (Ad). The purpose of this study was to analyze the clinical features and pulmonary function findings in children with PIBO. Cases caused by Ad were compared with cases in which no viral agent was identified. Methods: Fifty-eight children with PIBO were prospectively studied. Clinical data and pulmonary function tests (spirometry and plethysmography) were evaluated. Patients were divided in two groups according to the identification of the causal agent. Group 1 (G1): Adenovirus (+) Group 2: No etiologic agent identified. Results: Fifty-eight patients (male/female ratio 3.4:1); median age 8 years; mean age at initial injury 11 months; median time of hospitalization at acute stage of disease 60 days. Spirometry: FVC 68 +/- 13%, FEV1 40.5 +/- 11%, FMMF25-75% 16.7 +/- 7.5%. Pletysmography: TLC 136 +/- 22%, FRC 208 +/- 50%, RV 343 +/- 102%, RV/TLC 59 +/- 10, SGaw 0.05 +/- 0.02. When clinical, spirometric and plethymographic data were compared, no statistically significant difference was found between the two groups. Conclusions: PIBO is an extremely crippling lung disease with significant obstructive pattern in PFT. Both analyzed groups shared similar characteristics in the acute phase of the disease and in the severity of the sequelar pulmonary disease. Pediatr Pulmonol. 2010; 45:1180-1185. (C) 2010 Wiley-Liss, Inc.