Purpose: The purpose of this paper is to conduct an in-depth quantitative and qualitative evaluation of a family-based weight loss and healthy life style programme for clinically obese children in England. Design/methodology/approach: The mixed method case study evaluation used included obtaining pre and post measurements of anthropometry and a range of attitude and behavioural attributes. The qualitative phase of the study involved in-depth interviews and focus groups. Findings: The programme is demanding and resource intensive and designed as an intervention for children needing most help with their weight. Participants included the families of five referred children (n = 18 individuals) and the intervention team (n = 7). All but one child had reduced BMI centiles at the end of the programme. There were also improvements to a number of self-report aspects of healthy eating and levels of activity and quality of life, self-esteem and levels of depression indicators. The qualitative evaluation generated a number of insightful data themes. Research limitations/implications: Limitations include the case study design and small sample numbers. Also weight loss is an important indicator of any weight management programme's success however the short length of time programme was run is a barrier to seeing any substantive changes in any of the participating children's weights. Practical implications: The evaluation conducted gives insights into the positive aspects of the programme and can inform development of similar programmes. Originality/value: There are few examples of in-depth and comprehensive quantitative and qualitative approaches used to evaluate this type of intervention. (Contains 5 tables.)