BACKGROUND The obesity surgery mortality risk score (OS-MRS) is a five-point scoring system stratifying the risk of post-operative mortality. Patients with a body mass index (BMI) > 60 may also carry an increased risk of peri-operative complications. Laparoscopic sleeve gastrectomy (LSG) as an initial procedure could reduce weight and associated comorbidity allowing a safer, definitive second procedure. We investigated weight loss and risk reduction in patients having LSG as part of a planned two-stage definitive bariatric procedure. METHODS Patients with a high OS-MRS (4-5), males with BMI > 60 or females with BMI > 65, who underwent LSG were identified from a prospective database. Data were analysed by means of the Mann-Whitney U and Chi-squared test. RESULTS Sixty-eight patients underwent LSG. LSG reduced median BMI at 12 months (68 versus 54, P < 0.001) and the OS-MRS (3 versus 2, P = 0.005). An increase in patients considered low risk (OS-MRS, 0-1) was seen following LSG (35% versus 14%, P = 0.006). The proportion of patients with BMI < 50 increased from 0% to 30% (P < 0.001). Improvement or resolution of diabetes and hypertension was seen in 23% and 25% of cases, respectively. CONCLUSIONS LSG achieves good weight loss, reduces the OS-MRS and improves obesity-related comorbidity in high-risk surgical patients.