The effects on fetal growth of iatrogenic prescription for dietary restriction in pregnancy have been infrequently assessed, and results have suggested large decrements in birthweight. We therefore related maternal dietary restriction to fetal growth among participants in the National Collaborative Perinatal Project at the Columbia Presbyterian Medical Center in New York. There were 255 women who delivered term infants with birthweights under the 31st percentile (low birthweight), who were each matched to women who delivered heavier term infants, within ethnic and gestational age strata. On review of antenatal records, 198 women were identified who had received a physician's recommendation to restrict caloric intake to 1800 kcal/day or below. The odds ratio between caloric restriction and low birthweight was 0.88 (not significant [NS]). Rates of maternal weight gain were controlled by linear multiple regression analysis, since higher weight gain was associated both with the likelihood of having a diet prescribed and with higher birthweight. With control for weight gain, although the odds ratio was reversed, the change was of small magnitude and not statistically significant. We found no relationship between medical advice to limit caloric intake during pregnancy and intrauterine growth retardation. Since women asked to limit caloric intake continued to gain more weight than others, the results are consistent with lack of compliance with the dietary regimen.