BACKGROUND: Bone mineral density (BMD) measurements are the standard tool in the diagnosis of osteoporosis. However, recent developments in bone research show that a BMD measurement, while still important in a clinical setting, is in itself insufficient to accurately predict fracture risk or measure treatment effects of an antiosteoporosis drug. Clinical experience with patient follow-up strongly suggests that bone quality must also be taken into account. OBJECTIVES: The objectives of this paper are. (1) to describe the determinants of bone strength (structural and material properties of bone, both of which are affected by bone turnover) and their interrelationships, and (2) to provide a schematic explanation of these determinants of bone strength, which in this paper is referred to as the Bone Quality Framework. METHODS: Relevant information from the primary literature and review articles published in the English language were identified through a MEDLINE search of the medical literature, from 1990 to October 2004, in the fields of bone density, bone strength, bone quality, fracture risk, and fracture risk reduction. Additional publications were identified from the reference lists of the resulting articles. Identified publications relevant to the objectives of this review paper were selected. CONCLUSIONS: The Bone Quality Framework is presented in this paper as a means of summarizing and explaining the determinants of bone strength. In this framework, bone quality can be understood as an umbrella term that describes the set of characteristics that influence bone strength and explains the interrelationships of these characteristics. Bone strength depends on the structural and material properties of bone, both of which are influenced by the rate of bone turnover. Not all determinants of bone strength are well represented by a BMD measurement. The Bone Quality Framework presents an opportunity to examine all the determinants of bone strength. Greater understanding of the concept of bone quality will ultimately help improve the assessment of fracture risk and monitoring of patients receiving treatment for osteoporosis.