OBJECTIVE From a continuing investigation of the clinical performance of three different types of composite resin, the findings of the clinical evaluation at 8 years are presented. METHODS One operator placed 330 restorations in Class I and Class II preparations in the posterior teeth of 72 patients. Every patient received at least one restoration of each type of material: a microfilled composite, a small particle hybrid, a relatively coarse particle hybrid, and an amalgam control. Restorations were evaluated using clinical criteria. RESULTS Forty six patients attended the 8-year recall. Twenty-five of the 213 restorations (13.7% of the composites and 5.8% of the amalgams) originally placed in these 46 patients had previously failed or been lost from the study or were assessed as requiring replacement at the 8-year recall. Bulk fracture and secondary caries at the margin were the most common forms of failure in the composite restorations. Other failures or losses were associated with a non-margin defect in the composite, caries not associated with the restoration, pulpal considerations, extraction for orthodontics and reasons unknown. One-hundred and ninety-three restorations (including five that required replacement) were available for clinical evaluation at 8 years and these included 17 Class II restorations. Significantly fewer restorations placed with the coarse particle hybrid exhibited evidence of marginal deterioration. CONCLUSIONS At 8 years, composite restorations in posterior teeth had failed at a rate two to three times that of amalgam restorations. The most common types of failure were bulk fracture and secondary caries at the margin.