Background: Iron deficiency anemia is a common finding in patients who undergo Roux-en-Y gastric bypass (RYGBP) for morbid obesity. This is the result of altered absorption but may also be compounded by occult losses. The present study evaluates risk factors for the development of anemiaMethods: A retrospective analysis of patients undergoing Roux-en-Y gastric bypass (RGB) from January 2003 to November 2007 was performed. All patients had a preoperative body mass index (BMI) > 40 kg/m2. A total of 200 patients were evaluated. All patients were given daily ferrous sulfate tablets supplements two weeks following operation. Hematological and metabolic indices were routinely evaluated following surgery. Patients were followed for a minimum of 80 weeks. Chi Square analysis was utilized to determine statistical significance for categorical data.Results: There were 38 males and 162 females with an average age of 40.8. 21 patients (11 percent) developed post-operative anemia and 179 patients did not. Anemia was due to iron deficiency in all cases. The groups had similar demographics, surgical procedure and co-morbidities. Menstruating females (p <.02) and those with peptic ulcer disease (p <.01) were risk factors for the development of post-operative anemia.Conclusions: Iron deficiency anemia is a frequent problems following bariatric surgery. RGB surgery compounds occult blood loss. Increased ferrous sulfate supplementation may be necessary to prevent iron depletion in populations at increased risk for the development of anemia.