Inquiry was made into certain factors related or believed to be related to the occurrence of accidental poisoning of children by interviewing members of the families of 466 children reported as poison cases from the hospitals of Alameda and Contra Costa Counties, California. Two other groups, one drawn from the birth certificate files, and one selected from families residing near the families of the poisoned children, were interviewed for comparison. The poison cases were similar in most respects to those reported previously in the literature. The risk of poisoning reached an abrupt peak at 29 months of age and was slightly higher for boys than for girls. Aspirin and other drugs were the offending materials in two-thirds of the cases. Mothers were responsible for the supervision of the poisoned child in over 80% of the events. The families of the poison case group and the comparison groups were more remarkable in their similarities than in their differences. Although they were similar in composition, the parents of the poisoned children were, on the average, 3 to 5 years younger than the parents of the comparison group families. The mothers of the poisoned children were 3 times as likely to have jobs outside the home as were the mothers in the comparison group. The families of the poison cases reported previous similar incidents involving their children more often than the families of the comparison groups. This study indicates to some degree the complexity of the factors that apparently influence the risk of childhood poisoning other than simply the availability and accessibility of toxic materials.