Different intervention strategies can prevent new cases of type 2 diabetes (T2DM) in obese subjects. The present systematic review and meta-analysis evaluates the effectiveness of different strategies in prevention of type 2 diabetes in obese subjects. Studies were grouped into five different strategies: (1) physical activity +/- diet; (2) anti-diabetic drugs (glitazones, metformin, glinides, alfa-glucosidase inhibitors); (3) antihypertensive drugs (ACE inhibitors, ARB); (4) weight loss-promoting drugs and lipid-lowering drugs (orlistat, bezafibrate, phentermine/topiramate controlled release); and (5) bariatric surgery. Only controlled studies, dealing with subjects BMI > 30 kg/m2, were included in the analysis, whether randomized or non-randomized studies. Appropriate methodology (PRISMA statement) was adhered to. Publication bias was formally assessed. Eighteen studies (43,669 subjects, 30,774 with impaired glucose tolerance and/or impaired fasting glucose), published in English language as full papers, were analyzed to identify predictors of new cases of T2DM and were included in a meta-analysis (random-effects model) to study the effect of different strategies. Intervention effect (new cases of diabetes) was expressed as odds ratio (OR), with 95 % confidence intervals (CIs). In obese subjects, non-surgical strategies were able to prevent T2DM, with different effectiveness [OR from 0.44 (0.36-0.52) to 0.86 (0.80-0.92)]; in morbidly obese subjects, bariatric surgery was highly effective [OR = 0.10 (0.02-0.49)]. At meta-regression analysis, factors associated with effectiveness were weight loss, young age and fasting insulin levels. Publication bias was present only when considering all studies together. These data indicate that several strategies, with different effectiveness, can prevent T2DM in obese subjects.