Evidence shows that surgery for severe obesity in adults improves health and psychological functioning, and is cost-effective. Data on bariatric surgery for adolescents with severe obesity are extremely limited, with no evidence on cost-effectiveness. We evaluated the lifetime cost-effectiveness of bariatric surgery compared with no surgery in adolescents with severe obesity from the UK's National Health Service perspective. Eighteen adolescents with body mass index ≥40 kg m-2 who underwent bariatric surgery (laparoscopic Roux en Y Gastric Bypass [RYGB] [N = 9], and laparoscopic Sleeve Gastrectomy [SG] [N = 9]) at University College London Hospitals between January 2008 and December 2013 were included. We used a Markov cohort model to compare the lifetime expected costs and quality-adjusted life years (QALYs) between bariatric surgery and no surgery. Mean cost of RYGB and SG procedures were £7100 and £7312, respectively. For RYGB vs. no surgery, the incremental cost/QALY was £2018 (95% CI £1942 - £2042) for males and £2005 (95% CI £1974 - £2031) for females. For SG vs. no surgery, the incremental cost/QALY was £1978 (95% CI £1954 - £2002) for males and £1941 (95% CI £1915 - £1969) for females. Bariatric surgery in adolescents with severe obesity is cost-effective; it is more costly than no surgery however it markedly improved quality of life.