Five-year results from four centres of the multicentre clinical trial of the posterior composite Occlusin are reported. Data is presented in respect of 256 restorations of Occlusin and 69 restorations of a conventional lathe cut amalgam. It is concluded that more than 90 per cent of the restorations under investigation should be rated as clinically acceptable after five years in clinical service, that the wear resistance of the restorations of Occlusin, as assessed by the clinicians, was similar in preparations of different sizes and to that of the amalgam controls, and that similar clinical results were obtained irrespective of the technique used to achieve moisture isolation.