The relationship between changes in relative weight and fitness was assessed 5 years after children began treatment for obesity. Multivariate regression analysis showed that two factors were independently related to fitness change: (a) maintenance of weight loss from the end of 6 months of treatment to the 5-year follow-up and (b) initial fitness level. Children who showed the largest long-term changes in relative weight and the lowest initial fitness showed the largest improvements in fitness. Short-term weight loss was not related to long-term fitness change. These results show that weight loss and fitness are related over 5 years.