Fifteen very lew birth Height (VLBW) children, nine appropriate for gestational age (AGA, mean birth weight 1302±164 g, gestational age 30±1.5 weeks), and six stall far gestational age (SGA, mean birth weigth 1263±117 g, gestational age 35.3±1.5 weeks), were studied at the age of 7-12 years, and compared to twentysix age-, sex-, and height-matched healthy children, who were born at term (mean birth weight 3226±167 g). None of the VLBW children had developed chronic broncopulmonary disease. The habitual level of physical activity was not different in the VLBW and control group. Pulmonary function tests and progressive exercise tests on treadmill were performed. Forced vital capacity, forced expiratory volume at one second and forced expiratory flow between 25% and 75% of vital capacity were in the normal range for all the subjects. No differences were found in maximum oxygen consumption (VO2 max), anaerobic threshold (AT) and maximal heart rate between the ASA (VO2 max = 42.1±8.6 ml/min/kg, AT = 31.2±4.4 ml/min/kg) and SGA children (VO2 max = 43.4±11 ml/min/kg, AT = 34.2±8.5 ml/min/kg) and the respective controls (AGA controls VO2 max = 44.2±12.4 ml/min/kg, AT 31.8±4.2 ml/min/kg; SSA controls VO2 max =40.7±6 ml/min/kg, AT 29.8±2.2 ml/min/kg). Both in the AGA and SGA subgroups the preexercise VO2 values were comparable to those of the controls. In the SGA subgroup the energy cost of running throughout the test was significantly higher with resoect to the controls (ANOVA p<0.025), 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.