Adults with intellectual disabilities experience high rates of obesity. Despite this higher risk, there is little evidence on the effectiveness of weight-loss interventions for adults with intellectual disabilities and obesity. The present study examined the effectiveness of the TAKE 5 multi-component weight-loss intervention. Adults with obesity were invited using specialist intellectual disability services to participate in the study. Obesity was defined as a BMI of 30 kg/m2 or greater. TAKE 5 included a daily energy-deficit diet of 2510 kJ (600 kcal), achieved via a personalised dietary prescription. Participants' body weight, BMI, waist circumference and levels of physical activity and sedentary behaviour were measured before and after the intervention. A total of fifty-four individuals consented to participate, of which forty-seven (87 %) completed the intervention in the study period. There was a significant decrease in body weight (mean difference - 4·47 (95 % CI - 5·91, - 3·03) kg; P < 0·0001), BMI (- 1·82 (95 % CI - 2·36, - 1·29) kg/m(2); P < 0·0001), waist circumference (- 6·29 (95 % CI - 7·85, - 4·73) cm; P < 0·0001) and daily sedentary behaviour of participants (- 41·40 (95 % CI - 62·45, - 20·35) min; P = 0·00 034). Of the participants who completed the intervention, seventeen (36·2 %) lost 5 % or more of their initial body weight. Findings from the study suggest that TAKE 5 is an effective weight-loss intervention for adults with intellectual disabilities and obesity. The effectiveness of TAKE 5 should be examined further in a controlled study.