Secondary osteoporosis is a common cause of osteoporosis, and there are many medical conditions associated with osteoporosis. Many of these present well before osteoporosis develops, and knowledge of these pre-existing conditions may influence the decision about whether to test and/or treat for osteoporosis. Men and premenopausal women with unexplained osteoporosis or a history of fragility fracture should undergo investigation for secondary osteoporosis. Postmenopausal women with risk factors for secondary osteoporosis should also be carefully evaluated. Beyond the well-recognised association with glucocorticoids, an increasing list of drugs has been implicated in causing bone loss and fractures. With appropriate consideration of secondary causes and relevant investigations, many of these conditions are preventable with newer therapies.