In intact fresh cadaver specimens, we experimentally studied angular and rotatory deformities at the distal and middle levels of the forearm. The remaining pronation and supination motions were measured. When both bones of the forearm were angulated with a combined deformity (radio-ulnar or dorsovolar, or both) of 10 degrees, a loss of pronation-supination of 12.5 +/- 4.5 per cent occurred in the forearms with a distal-third fracture; in the forearms with a middle-third fracture the average loss was 16.0 +/- 5.7 per cent. Pronation losses were similar for both distal and middle-third deformities. However, supination losses were much less affected (p less than 0.01) in forearms with deformities at the distal-third level while the losses were considered drastic for middle-third deformities. Rotatory deformities produced losses of pronation-supination that were equal to the degree of deformity. Clinical Relevance: Study of the artificially created deformities in cadavera indicated that angular and rotatory deformities of the forearm of 10 degrees or less result in minimum limitation of pronation-supination. These degrees of limitation of motion in clinical practice are easily compensated for and are cosmetically acceptable. The fact that the perfect anatomical restoration of fracture alignment that often is obtained with internal fixation does not always result in complete restoration of motion suggests that: (1) this residual impairment of function is due to soft-tissue scarring, and (2) the mild angular and rotatory deformities resulting from nonsurgical treatment of fractures of the forearm may produce limitations of motion of an equally acceptable degree.(ABSTRACT TRUNCATED AT 250 WORDS)