A patient with morbid obesity and several psychiatric comorbidities underwent laparoscopic sleeve gastrectomy and experienced success with weight loss. However, she experienced lightheadedness, nausea, and a fall and was admitted to the hospital for encephalopathy due to lithium toxicity. The pharmacokinetics of lithium is altered following bariatric surgery. Due to these factors, adjustments were made to the patient's lithium therapy, her levels were subsequently reduced into the therapeutic range, and she continued with no further issues. Mechanisms of lithium toxicity following bariatric surgery and a monitoring protocol to prevent toxicity are discussed.