Introduction: The present study describes a randomised controlled trial (RCT) based on a novel, generalisable intervention for childhood obesity, comparing the intervention with a no-treatment control group. Method: The Malaysian Childhood Obesity Treatment Trial (MASCOT) was a single-blind RCT of a dietetic treatment for childhood obesity in children of primary school age (7 to 11 years old) in Kuala Lumpur, Malaysia. The MASCOT comprising eight sessions, of an 8-hour family-centred group treatment programme is described, based on behavioural change techniques. The study sample was characterised by BMI zscore, health related quality of life reported by participants and their parents (PedsQL questionnaire), objectively measured habitual physical activity and sedentary behaviour (Actigraph accelerometry) Results: The MASCOT sample of 107 children was characterised by a low quality of life, mean total score on PedsQL 67.7 (4.5) as reported by the children, and 66.0 (16.4) as reported by their parents. The children spent, on average, 89% of their waking day on sedentary activity, and 1% of the day in moderate-vigorous intensity physical activity, equivalent to only around 8 minutes/day. Conclusion: Obese children in the MASCOT study had an impaired quality of life, high levels of sedentary behaviour and very low levels of physical activity.