The longevity of 1,207 restorations placed by students was studied in 70 adult patients. The overall percentage of restorations lasting ten years or more (P10) was 75.4 percent and survival times were longer than in most previous restoration longevity studies. Cast restorations lasted significantly longer than amalgams, which in turn lasted significantly longer than composites. P10 values were 91.1 percent, 72.0 percent, and 55.9 percent, respectively. Analysis by surfaces involved indicated that single-surface lasted longer than multisurface restorations. The survival of restorations placed in patients aged 60 or more was less favorable (P10 = 56.8 percent) than for younger patients (P10 = 78.3 percent). A subset of the population was identified on the basis of a restoration failure rate of greater than 4.0 X 10(-2) failures/restoration year. This group, comprising 18.6 percent of the population, accounted for 56.1 percent of all restoration failures. The P10 value for this high-risk group was 55.8 percent, as compared with 83.9 percent for the remainder of the population.