Accidental poisoning in pre-school children requiring hospital admission has increased sixfold from 1955 to 1975 in the Stockholm area. The mortality from this accident has decreased from 0.5 to less than 0.1 per 100 000 pre-school children in the whole of Sweden during the same period. Medical and psychosocial background factors were investigated in 104 consecutive in-patients (0--6 years old) with accidental poisoning and compared to an out-patient group, a group of patients who only had called the poison control centre, and a matched control group from Child Health Centres. There were no difference between the groups regarding health and history of earlier accidents except that 20--25% of the families of the poisoned children and 7% of the control families had called the Poison Control Centre before. Change of residence during the last 6 months was much commoner among families of poisoned children than of nonpoisoned. Other social stress factors were more common among in-patients than out-patients. The measures taken by the parents to combat the poisoning were adequate in most cases. The decrease in mortality inspite of the increase in potentially dangerous accidental poisonings may be attributed to a good knowledge among parents about adequate measures and where to seek advice resulting in early treatment, and to intensive care and antidote therapy.