Background: Psoriasis is a chronic inflammatory disease of the skin with joint manifestations. Greater psoriasis severity and lower response to treatment have been linked to obesity. However, the effect of weight reduction by non-pharmacologic intervention on disease severity is still questionable. This is a systematic review and meta-analysis of randomized controlled trials (RCTs) on the effect of dietary and lifestyle weight loss interventions on psoriasis severity. Methods: We comprehensively searched PubMed/MEDLINE, EMBASE and CENTRAL from their inception to August 2014. Inclusion criteria were RCTs that examined lifestyle intervention by diet or exercise in overweight or obese patients with psoriasis and measured the severity of psoriasis as an outcome compared with controls. Two authors independently assessed article quality and extracted the data. Results: Out of 12 full-text articles, 7 RCTs involving 878 participants met our inclusion criteria. Five of these RCTs were included in the meta-analysis, which was based on the random-effects model. There was a greater reduction in the Psoriasis Area Severity Index (PASI) score in patients receiving weight loss intervention than in controls, with a pooled mean difference of -2.49 (95% confidence interval (CI), -3.90 to -1.08; P=0.004). More participants in the intervention group than in the control group achieved a 75% reduction in the PASI score, with a pooled odds ratio of 2.92 (95% CI, 1.39-6.13; P=0.005).