The objective in the Hungarian randomised double-blind controlled trial was to study the preventive effect of periconceptional multivitamin supplementation on neural tube-defects and other congenital abnormalities. There were 2,471 and 2,391 informative offspring (prenatally diagnosed and terminated malformed fetuses, stillborn fetuses, and liveborn infants) in the multivitamin and placebo-like trace element groups, respectively. A single tablet either of a multivitamin containing 0.8 mg of folic acid or trace element supplement was given daily for at least one month before conception and at least until the date of the second missed menstrual period. The total rate of major congenital abnormalities was 20.6/1,000 in the multivitamin and 40.6/1,000 in the trace element group. After the exclusion of six cases of neural-tube defects in the trace element group the difference was very highly significant [P = 0.0003; relative risk of 0.54 (95% CI 0.39, 0.76)]. Multivitamin supplementation appeared to result in a significant reduction in the rate of urinary tract abnormalities, mainly obstructive defects, and in the rate of sporadic cardiovascular malformations, mainly ventricular septal defects. This report is regarded as a hypothesis-generating study encouraging others to see if the result can be repeated.