We studied pulmonary function 1 year after neonatal respiratory distress (RD) in 54 infants who had been treated at birth in the same neonatal intensive care unit. RD was related to hyaline membrane disease in 36 cases (group I) and to other causes in 18 cases (group II). Compared with predicted values, dynamic lung compliance (CL) was lower (less than -2 SD) and total pulmonary resistance (RL) was higher (+2 SD) in 18 (33%) and 12 (22%) infants, respectively. The relationships between these functional abnormalities at 1 year of age and the characteristics of the neonatal respiratory disease were assessed using a multifactorial analysis (multiple correspondences analysis). We found that elevated RL (greater than +2 SD) at 1 year of age was very significantly related with hyaline membrane disease, involving both high rate of positive pressure ventilation and prolonged intubation, and with the presence of both tachypnea and abnormal chest X rays at the time of discharge. Compared with elevated RL, the relationships between low CL (less than -2 SD) and the same neonatal characteristics were less significant; in particular, there was no strong link between low CL and hyaline membrane disease. Finally, birth before 30 weeks gestation was an index of severity.