OBJECTIVE Pediatric patients on chronic hemodialysis (HD) are at high risk of inactivity and poor physical fitness. The aim of this study was to assess the main correlates of exercise capacity in a cohort of children and young adults on chronic HD. METHODS Twelve patients on chronic HD (median age 15.6 years; range 9.1-24.2) underwent a 6-minute walking test (WT), spirometry, a 1-minute chair stand test, and the measurement of lower extremity strength. Demographic data, anthropometry (dry weight, height, body mass index, and skinfold thickness, all expressed as standard deviation scores [SDS]), biochemistry (serum albumin, hemoglobin, creatinine, C-reactive protein, bicarbonate), bioimpedance analysis, HD adequacy indices (spKt/V and eKt/V), left ventricular mass index, and medications were also recorded. RESULTS There was a significant correlation among the distance covered during the WT (median 552 m, range 186-670), forced vital capacity (87.8% of predicted, range 49.7-136), forced expiratory volume in 1 second (86.7%, range 54.7-126.7), and peak expiratory flow (75.5%, 49.7-105.1). All of these indices positively correlated with the weight SDS (r 0.69-0.85), pre-HD serum creatinine (0.57-0.77), and serum albumin (0.60-0.77) and negatively correlated with weekly erythropoietin dose per kilogram of body weight (from -0.64 to -0.83), with P values ranging from <.05 to <.0005. Lower extremity strength (median 11.5 kg, range 3-15) positively correlated with the number of stands at the chair stand test (median 33, range 18-47; r 0.73, P < .05) and serum albumin (r 0.83, P < .01). Distance at the WT, forced vital capacity, lower extremity strength, and the number of stands at the chair stand test all negatively correlated with C-reactive protein levels (r from -0.81 to -0.67, P < .05). CONCLUSIONS Our findings show that protein-energy wasting and chronic inflammation are strongly correlated with the exercise capacity of children and young adults on chronic HD.