The increase in the number of bariatric procedures annually suggests that these patients will constitute an increasing portion of obese patients who require hospital and intensive care. Currently, little prospective information is available regarding the course of bariatric surgery patients requiring intensive care. Knowledge of the type of bariatric operation performed and an understanding of its anatomy and physiology are useful to provide optimal care to these patients, particularly when considering potential nutrition complications and their diagnosis and treatment. In this article, the authors describe nutrition problems that may be present and potentially affect the course of a hospitalized and/or critically ill patient who has previously undergone a bariatric operation.