Obesity is the most widespread nutritional problem globally. Bariatric surgery is the preeminent long-term obesity treatment. Bariatric procedures manipulate the intestines to produces malabsorption and/or restrict the size of the stomach. The most enduring bariatric procedure is the Roux-en-Y gastric bypass, which utilizes both restriction (small stomach pouch) and malabsorption (duodenum bypass). The in-vogue procedure is the vertical sleeve gastrectomy - resection of the greater curvature of the stomach (predominantly restrictive). Malabsorptive procedures function by decreasing nutrient absorption, primarily fat and fat-soluble nutrients (vitamins A, D, E, and K). Most studies of vitamin D status in bariatric surgery candidates reported a prevalence of over 50% vitamin D deficiency (<50 nmol/L), enduring post-operatively with one study reporting 65% deficient at 10 years post-bariatric surgery. Obesity is associated with chronic inflammation, which may contribute to adverse surgical outcomes, e.g. poor healing and infection. Since vitamin D deficiency is also associated with chronic inflammation, obese individuals with vitamin D deficiency have extraordinary risk of adverse surgical outcomes, particularly delayed wound healing and infection due to the role of vitamin D in re-epithelialization and innate immunity. When the risk of adverse surgical outcomes in obesity is combined with that of vitamin D deficiency, there is likely an additive or potentially a synergistic effect. Furthermore, deficiency in fat-soluble vitamins, such as vitamin D, is considered a metabolic complication of bariatric surgery. Thus, determining the vitamin D status of bariatric surgery candidates and amending it preoperatively may prove greatly beneficial acutely and lifelong.