Pulmonary function was measured in 35 patients (mean age 11.6 years) with simple complete transposition 4.4 years after intracardiac repair. A disturbance in the lung function (greater than 2 SD from the normal value) was found in 88% of the patients. A marked increase in static recoil pressure (P less than 0.001) was most frequent (in 66%). Static lung compliance was only 75.1% of the predicted values. Values of mean vital and total lung capacity were decreased (P less than 0.01 and 0.001). Residual volume, the ratios of functional residual versus total lung capacity and residual volume versus total capacity were all increased. The signs of decreased patency of the airways were found in only 4 patients. A negative correlation was detected between the indices of lung stiffness and the age of assessment of lung function. A positive correlation was found between the ratios between functional residual and total capacity and pulmonary blood flow. No other correlation between lung function data and pulmonary arterial pressure or flow was proved. Increased lung stiffness, restriction of lung volume and hyperinflation could influence unfavorably the long-term results in successfully treated patients with simple complete transposition.