Fifteen very low birth weight children, 9 appropriate for gestational age (AGA, mean birth weight 1302 +/- 164 g) and 6 small for gestational age children (SGA, mean birth weight 1263 +/- 117 g), were studied at the age of 7-12 years, and compared to a group of 26 healthy, age-, sex-, and height-matched children born at term. None of the VLBW children had developed chronic bronchopulmonary disease. Pulmonary function tests and progressive exercise tests on a treadmill were performed. Forced vital capacity, forced expiratory volume at 1 s and forced expiratory flow between 25% and 75% of vital capacity were normal for all subjects. No differences were found in maximum oxygen consumption, anaerobic threshold and maximal heart rate between the AGA and SGA children and the respective controls. Both in the AGA and SGA subgroups, the pre-exercise oxygen uptake results were comparable to those of the controls. In the SGA subgroup the energy cost of running was significantly higher with respect to the controls, while no difference was found between the AGA and the control children. In conclusion, children with birth weight less than 1501 g have normal values of aerobic fitness. In SGA children the efficiency of running is slightly reduced.