From 1988 to 1994 a consecutive series of 1000 fractures of the adult clavicle was treated in the Orthopaedic Trauma Clinic of the Royal Infirmary of Edinburgh. In males, the annual incidence was highest under 20 years of age, decreasing in each subsequent cohort until the seventh decade. In females, the incidence was more constant, but relatively frequent in teenagers and the elderly. In young patients, fractures usually resulted from road-traffic accidents or sport and most were diaphyseal. Fractures in the outer fifth were produced by simple domestic falls and were more common in the elderly. A new classification was developed based on radiological review of the anatomical site and the extent of displacement, comminution and articular extension. There were satisfactory levels of inter- and intraobserver variation for reliability and reproducibility. Fractures of the medial fifth (type 1), undisplaced diaphyseal fractures (type 2A) and fractures of the outer fifth (type 3A) usually had a benign prognosis. The incidence of complications of union was higher in displaced diaphyseal (type 2B) and displaced outer-fifth (type 3B) fractures. In addition to displacement, the extent of comminution in type-2B fractures was a risk factor for delayed and nonunion.