Randomized clinical trials are the key source of information about the efficacy of drugs used in the prevention and treatment of osteoporosis. Currently, the measures of efficacy used in clinical trials in osteoporosis vary considerably from trial to trial, making it difficult to judge the relative efficacy of different therapies or pool results in metaanalyses. This is particularly important, since few direct “head to head” comparisons of active agents exist in the literature or are likely to be performed, and many studies are too small to answer some types of questions on their own, such as the effect of treatment on fracture rates. For these reasons it would be useful for trials to share a set of measures that would allow comparisons and pooling of results.