Background. Increased malnutrition and morbidity among Iraqi children after the onset of the Persian Gulf war have been reported by several fact-finding missions. The magnitude of the effect of the war and the economic embargo on child mortality remains uncertain, however. Methods. We conducted a survey of 271 clusters of 25 to 30 households each, chosen as a representative sample of the Iraqi population. The households were selected and the interviews conducted by an international team of public health professionals independent of Iraqi authorities. In each household all women 15 to 49 years of age were interviewed, and the dates of birth and death of all children born on or after January 1, 1985, were recorded. Results. The study population included 16,076 children, 768 of whom died during the period surveyed (January 1, 1985, to August 31, 1991). The age-adjusted relative mortality for the period after the war began, as compared with the period before the war, was 3.2 (95 percent confidence interval, 2.8 to 3.7). No material change in the relative risk was observed after adjustment for region of residence, maternal education, and maternal age. The increase in mortality after the onset of the war was higher among children 1 to less than 12 months old (relative risk, 4.1; 95 percent confidence interval, 3.3 to 5.2) and among those 12 to less than 60 months old (relative risk, 3.8; 95 percent confidence interval, 2.6 to 5.4) than among those less than 1 month old (relative risk, 1.8; 95 percent confidence interval, 1.4 to 2.4). The association between the war and mortality was stronger in northern Iraq (relative risk, 5.3) and southern Iraq (relative risk, 3.4) than in the central areas (relative risk, 1.9) or in Baghdad (relative risk, 1.7). Conclusions. These results provide strong evidence that the Gulf war and trade sanctions caused a threefold increase in mortality among Iraqi children under five years of age. We estimate that an excess of more than 46,900 children died between January and August 1991.