Use of modified cavo-surface angles (CSAs) and finishing techniques for amalgam restorations may influence the long term marginal fracture around these restorations. One operator placed 111 Tytin amalgam restorations in Class I and II preparations in the permanent teeth of 37 patients, each of whom received three restorations. One of these restorations was placed in a cavity prepared with a 'traditional' CSA and was finished more than 24 h after placement. Prepared cavities for the remaining two restorations for each patient were 'modified' with the aim of producing an occlusal CSA of 90-110 degrees. One restoration was carved-only and the other was finished more than 24 h after placement. Clinical evaluation of the restorations was carried out at baseline, 1 year and 2 years. At these times, the restorations were photographed and stone replicas were obtained from impressions taken at the cavity preparation stage to determine the cavo-surface angles. Careful application of the modified cavity design provided a mean cavo-surface angle of 109 degrees whereas a 'traditional' cavity design provided a mean cavo-surface angle of 126 degrees. Using the Mahler photographic method of evaluation, a combination of modification of the occlusal cavo-surface angle and finishing of the restoration was found to have an influence on the marginal fracture at 2 years. The clinical significance of these findings, with respect to the modified cavity design, is discussed.