A 48-year-old woman was seen at the endocrinology clinic for generalized weakness 6 years after Roux-en-Y gastric bypass for morbid obesity (preoperative height, 1.63 m; weight 113.4 kg; and body mass index [BMI], 42.7 [calculated as weight in kilograms divided by height in meters squared]). After an initial postoperative weight loss, her weight plateaued, but 2 years prior to presentation, she developed chronic, oily diarrhea accompanied by new, gradual weight loss. Gastrointestinal evaluation including upper and lower endoscopies had been unremarkable, and her symptoms failed to improve after a trial of antibiotics for presumed bacterial overgrowth; pancreatic enzymes were not tolerated because of worsening gastrointestinal symptoms. She also reported 6 months of weakness climbing stairs and carrying objects, which limited her activity. On examination, she weighed 49.8 kg (BMI, 18.9) and bilateral upper and lower proximal muscle weakness was present. On evaluation, her laboratory values were 2.2 g/dL for albumin (to convert to grams per liter, multiply by 10); 3 mg/dL for serum urea nitrogen (to convert to millimoles per liter, multiply by 0.357); and 18 U/L for amylase, 12 U/L for lipase, 27 U/L for creatine kinase, 50 U/L for alanine transaminase, and 62 U/L for aspartate transaminase (to convert to microkatals per liter, multiply by 0.0167). Oral supplementation with high-protein liquids, vitamins A and D, and a multivitamin was initiated.