This prospective study evaluated 60 reproductive-age and postmenopausal women with lumbar disc disease to demonstrate the short-term effects of lumbar disc surgery on bone mineral density (BMD). Lumbar BMD was measured preoperatively and 3 months postoperatively by dual-energy X-ray absorptiometry (DEXA). Surgery was performed at only one level (L3-L4) and consisted of partial hemilaminectomy, discectomy, and, if necessary, partial facetectomy. Before surgery, 50% of the patients had osteopenia, and 31.7% had osteoporosis. After surgery, BMD decreased 5.5% in L3 vertebrae (P=.07), 14% in L4 vertebrae (P=.003), and 4.6% in L1-4 (P=.039). Six of 11 patients with normal BMD before surgery became osteopenic postoperatively; 9 of 30 women with osteopenia fulfilled criteria for osteoporosis after surgery. Reproductive-age and postmenopausal women undergoing surgery for lumbar disc disease are at risk of bone loss and should be spared an extensive procedure, which can further increase the amount of bone lost. All women for whom a surgical intervention is planned should be evaluated by DEXA preoperatively and postoperatively.