In the course of a prospectively designed long-term clinical trial, composite fillings and inlays were evaluated for clinical acceptability as restorative materials in one, two or more surface cavities of posterior teeth over a 1-year period. In 45 patients, 88 restorations were placed by nine student operators, under the supervision of an experienced dentist, to compare the two half sides using the composite resins Tetric (Vivadent), blend-a-lux (Blend-a-med), and Pertac-Hybrid Unifil (Espe). The first clinical follow-up check took place within a time period of 11-13 months after placement of the restorations using modified USPHS criteria. The interpretation of the clinical criteria showed satisfactory results over this time period: more than 85% of the inlays and direct fillings were rated "alpha" or "bravo", using the parameters of assessment defined in this study. Only three restorations (two fillings, one inlay), all in molars, were rated "delta", i.e., unacceptable. The reasons for their replacement were marginal opening, secondary caries, and loss of sensitivity. For the criteria "surface texture", "anatomical form of the surface", and "occlusion", composite inlays were significantly better than composite fillings. These results indicate that posterior composite restorations provide acceptable and excellent clinical service, even if they are placed by relatively inexperienced student operators.