The insulin-sensitizing thiazolidinediones (commonly known as glitazones) are an important and widely prescribed class of antidiabetic agents. Glitazones exert their action through activation of proliferator-activated receptor gamma (PPAR-gamma) nuclear transcription factor and are effective drugs to achieve glycaemic control in patients with type 2 diabetes mellitus. Recent rapidly growing evidence suggests that glitazone use is associated with accelerated bone loss and an increased risk of fracture. This review aims to evaluate the current knowledge of adverse effects of glitazone therapy on the skeleton. Articles in English, Spanish, German and French published up until April 2009 are included. Results from preclinical studies have demonstrated that activation of PPAR-gamma inhibits bone formation by primarily diverting mesenchymal stem cells to the adipocytic rather than to the osteogenic lineage, and that glitazones may increase bone resorption by stimulating osteoclasts. Numerous studies in humans have demonstrated decreased bone turnover, accelerated bone loss and impaired bone mineral density both in healthy volunteers and in patients with type 2 diabetes. Furthermore, results from recent large, randomized controlled trials and from observational studies provided evidence for an increased fracture risk for glitazone users, mostly for women, but possibly also for men. As a consequence of these observations, clinicians should carefully assess the fracture risk in patients with type 2 diabetes before starting therapy with glitazones.