OBJECTIVE: to investigate the differential effects of aerobic graded exercise and progressive resistance training on exercise tolerance, fatigue and quality of life in adolescent patients with chronic fatigue syndrome (CFS). DESIGN: single-blind, randomized controlled pilot trial. SETTING: a major metropolitan hospital in Melbourne, Australia. SUBJECTS: twenty-two adolescents aged 13-18 years diagnosed with CFS and admitted to the inpatient chronic fatigue rehabilitation programme. INTERVENTION: patients were randomized to either graded aerobic exercise training or a progressive resistance training programme, for five days/week for four weeks. The graded aerobic training consisted of 20-40 minutes of stationary cycling and treadmill exercise. The progressive resistance training involved 16 exercises performed with single set, moderate load and high repetitions. MAIN MEASURES: exercise tolerance (time to fatigue) measured on a graded sub-maximal treadmill test, metabolic equivalents and quality of life, along with muscular strength (maximium push-ups) and endurance (sit-to-stand) and questionnaires evaluating depressive symptoms and fatigue severity. RESULTS: no intervention was significantly better than the other for any outcome. However, physical capacity and quality of life significantly improved in both groups, while fatigue severity and symptoms of depression improved only with aerobic training. CONCLUSIONS: resistance and aerobic training resulted in similar changes to physical capacity, quality of life and fatigue severity. Generally, patients who completed resistance training or aerobic training experienced significant improvements in outcomes from baseline when they entered the programme. Whether these improvements can be attributed to the treatment is unknown.