A 52-yr-old white female presented with worsening low back and hip pain, associated with lower limb proximal muscle weakness and a waddling gait. Her laboratory evaluation revealed hypocalcemia, hypophosphatemia, a very low 25-hydroxyvitamin D level of less than 5 ng/mL, and a bone mineral density in the osteoporotic range. Her laboratory studies were consistent with osteomalacia, although this diagnosis was not established by histomorphometry. She avoided dairy products, spent little time outdoors, and when she went out, she covered her face, arms, and legs. She was on no medication. Her workup for malabsorption including sprue was negative. She was treated with calcium plus high-dose vitamin D 600,000 IU intramuscularly twice witihin 2 mo and had an impressive clinical improvement. Her difficulty with ambulation improved within 1 wk of start of therapy. Her bone mineral density increased by 40% at the spine and 35% at the hip at 4 mo of therapy, by 63% and 39% at 10 mo, and by 62% and 52% at 15 mo at these sites, respectively. Treatment of osteomalacia is extremely rewarding, with dramtic clinical improvement and normalization of bone mineral density.