INTRODUCTION: This study aimed to evaluate the LITE (Lifestyle Intervention for TEenagers) group programme, a family-based behavioural lifestyle intervention for overweight and obese adolescents. METHODS: We conducted a two-arm randomised controlled trial that recruited overweight and obese adolescents who attended a tertiary care weight management clinic. Participants were randomised to the LITE programme or usual care. The primary outcome assessed was body mass index (BMI) z-score. Secondary outcomes of anthropometric measurements, metabolic profile, parenting and adolescents' perception of family support were measured at baseline, three months and six months. Feasibility and acceptability of the LITE programme were also evaluated. RESULTS: 61 adolescents were enrolled, with 31 in the LITE programme and 30 in usual care. At three months, participants in the programme had a greater reduction in weight (-0.18 ± 2.40 kg vs. 1.48 ± 1.97 kg; p = 0.107), waist circumference (-1.0 ± 3.1 cm vs. 2.4 ± 2.7 cm; p = 0.016), waist-height ratio (-0.01 ± 0.02 vs. 0.01 ± 0.02; p = 0.040) and systolic blood pressure (-3.8 ± 13.7 vs. 5.7 ± 13.1; p = 0.119) compared to the usual care group. There was no significant difference in BMI z-score. At six months, there were significant improvements in adolescents' perception of family support for eating habits in the LITE group compared to the usual care group. The LITE programme had a good attendance rate of 67.7% and was well received. CONCLUSION The LITE programme showed feasibility and short-term clinical effectiveness in improving some clinical outcomes and improved adolescents' perception of family support.