The purpose of this study was to determine if the functional capacity and quality of life of children receiving treatment against acute lymphoblastic leukemia (ALL) is decreased compared to healthy age and gender-matched children. Functional capacity was assessed with a number of measurements as the peak oxygen uptake (VO2peak) and ventilatory threshold determined during a ramp treadmill test, functional mobility (Timed Up and Down Stairs test [TUDS]) and ankle dorsiflexion passive and active range of motion (passive and active DF-ROM, respectively). Quality of life (QOL) was determined with the Spanish version of the Child Report Form of the Child Health and Illness Profile-Child Edition (CHIP-CE/CRF). Fifteen children (9 boys, 6 girls; mean [SD] age: 6.8 +/- 3.1 years) receiving maintenance therapy against ALL were studied and fifteen, nonathletic healthy children (9 boys, 6 girls; 6.9 +/- 3.3 years) were selected as controls. The mean values of VO2peak and active DF-ROM were significantly (p < 0.05) lower in patients (25.3 +/- 6.5 ml . kg (-1) . min (-1) vs. 31.9 +/- 6.8 ml . kg (-1) . min (-1) in controls and 19.6 +/- 8.0 degrees vs. 24.1 +/- 5.0 degrees , respectively). Children's self report of satisfaction (with self and health) (p < 0.05), comfort (concerning emotional and physical symptoms and limitations) (p < 0.01) and resilience (positive activities that promote health) (p < 0.01) were significantly decreased in patients with ALL. In summary, children receiving treatment against ALL have overall lower functional capacity and QOL than healthy children. However, their physical condition and health status are sufficiently high to allow them to participate in physical activities and supervised exercise programs.