A 48-year-old woman underwent jejunoileal bypass surgery for obesity while hypercalcemic. Three years later, she developed symptomatic osteomalacia impairing her daily activities. Bone biopsy confirmed the clinical diagnosis of osteomalacia, and treatment with 8000 U daily of vitamin D and milk resulted in striking improvement of clinical symptoms and resolution of her osteomalacia both chemically and histologically. The patient, however, again became hypercalcemic and a parathyroid adenoma was subsequently removed with restoration of serum calcium values to normal. Neither the occurrence and successful treatment of gross symptomatic osteomalacia consequent to Jejunoileal bypass surgery, nor the obscuration of primary hyperparathyroidism by osteomalacia has been hitherto well documented in the United States.