Fifteen per cent of acute fractures of the scaphoid waist fail to unite if treated non-operatively in plaster, resulting in persistent loss of function. Suspected risk factors for non-union include proximal fracture fragment avascularity and assessments of fracture displacement and comminution. This series of studies investigated whether one can accurately identify which scaphoid waist fractures will unite with plaster treatment. They suggest that proximal fracture fragment vascularity is not a predictor of outcome. In contrast, assessments of fracture displacement on magnetic resonance imaging (MRI) and computed tomography (CT) but not scaphoid series radiographs can be used to predict outcome. Undisplaced fractures are benign and unite reliably with 4-8 weeks' treatment in plaster. Displaced fractures with 3mm or more gapping have a significant nonunion rate if treated in plaster and might be better treated operatively. Use of MRI/CT may allow reliable, cost effective treatment of acute fractures through the scaphoid waist.