With the proliferation of bone densitometers, an increasing number of premenopausal women are having their bone density tested. Approximately 15% of premenopausal women have bone mineral density that is more than 1 standard deviation less than the young-adult mean, and approximately 0.6% are more than 2.5 standard deviation below young-adult mean bone density. Most pre-menopausal women with low bone density have low peak bone mass, stable bone density, and low short-term absolute risk of fracture. The management of these patients involves nonpharmacologic lifestyle measures and reassurances that fracture risk is low. A minority of premenopausal women with low bone density have increased short-term absolute fracture risk with contributing diseases, conditions, or medications that should be identified and treated. Premenopausal women with fractures are at increased risk for fractures later in life. Methods for evaluating these patients and selecting those who require additional care are reviewed.