Objectives. Clinically-relevant protocols for the treatment of childhood obesity are lacking. This study report results for a clinic-based structured treatment program for chronic childhood obesity. Methods. Patients were measured at baseline and for up to 24 months; there were no prior eligibility criteria. At baseline, height, weight, Tanner stages, testicular size, time of menarche, and social class of the parents were registered. A structured, tailored treatment plan including best-practice-based interventions was initiated. Height, weight, and pubertal development were measured at subsequent visits. Results. A total of 617 children or youths were included; 325 were girls and 292 were boys. At entry, the mean age was 11.6 years and the mean body mass index (BMI) standard deviation score (SDS) was 3.0. Seventy stopped treatment, 547 were in treatment, 125 had 1 examination, and 492 had two or more examinations, with a mean visit interval of six weeks. After 12 months, the mean BMI SDS decreased by 0.23 (P < 0.0001) in girls and by 0.32 (P < 0.0001) in boys. After one year, the retention rate was 90.2%, and 68.7% had reduced BMI SDS. After two years, the retention rate was 75.0%, of which 62.5% had reduced BMI SDS. The reductions in BMI SDS were independent of baseline adiposity, age (in boys), puberty stage, and social class, but were dependent on sex, age (girls), and place of referral. Conclusions. This clinical obesity treatment was safe and effective in reducing BMI SDS independent of baseline adiposity, age (boys), or social class in these young people.