In this study of 100 patients with established hand osteoarthritis (OA) and 100 matched controls, clinical thumb base OA was more common in subjects with features of articular hypermobility. Hypermobile patients also had more severe thumb base involvement and more disability, but less interphalangeal joint OA. This trend was evident even in patients with moderate laxity (Beighton score > or = 2), and there was a significant correlation between disability and the number of hypermobility criteria. The majority of patients who had their initial symptoms from the first carpometacarpal joint, and those who had severe OA in that joint, had hypermobility features. This study indicates a relationship between hypermobility and the development of thumb base OA, and suggests that 'hypermobility-associated OA' may be a hitherto unrecognized subset of hand OA.