A suburban Ontario community hospital encountered 21 ± 1 overdoses of children's multiple vitamins yearly between 1978 and 1981. Of these, 35% involved one particular cartoon character preparation. Parents were surveyed to determine whether this particular preparation resulted in a disproportionate number of accidental overdoses. However, the use of vitamins with a cartoon character format did not lead to a greater risk of overdose than did conventional preparations. Of the 1051 families who had given multiple vitamins to their children 34 (3%) had experienced an overdose. The number of vitamin preparations used by each family was the most powerful determinant of overdose (p < 0.001). The risk of accidental overdose increased from 1.5% with one multiple-vitamin preparation to 8% with four or more preparations. Among all the variables examined, exposure was the most important element in the risk of multiple-vitamin overdose.