Pulmonary function was evaluated in both infancy and childhood in the same 19 prematurely born infants, who required mechanical ventilation (MV) during the neonatal period. Results of our patients were compared with those of control subjects. Upon first evaluation, we found that lung resistance (RL) was significantly elevated (24.85 +/- 6.06 vs. 17.77 +/- 2.39 cmH2O/L/s; P less than 0.01). The mean value of dynamic lung compliance (CLdyn) was low, but the difference compared to controls did not reach significance. From infancy to childhood, elevated RL persisted (9.33 +/- 2.51 vs. 6.52 +/- 1.52 cm H2O/L/s; P less than 0.01), and the decrease of CLdyn became significant (46.86 +/- 12.84 vs. 59.34 +/- 15.68 mL/cmH2O; P less than 0.05). In addition, maximum flow at functional residual capacity was significantly decreased (0.824 +/- 0.284 vs. 1.215 +/- 0.358 L/s; P less than 0.01); whereas pulmonary diffusing capacity for carbon monoxide was similar in the patients (7.62 +/- 2.16 mL/min/mm Hg) and in the controls (8.38 +/- 1.6). Pulmonary dysfunction following premature birth, respiratory distress, and prolonged MV may not resolve from infancy to childhood.