Objective:To test the hypothesis that strict control of diabetes during pregnancy can reduce the risk for neonatal hypocalcemia in infants of diabetic mothers.Methods:One hundred thirty‐seven pregnant women with insulin‐dependent diabetes enrolled before 9 weeks' gestation were randomized to one of two treatment groups. In 68 subjects, the goals were fasting blood glucose level less than 4.44 mmol/L (80 mg/dL) and 1.5‐hour postprandial blood glucose level less than 6.66 mmol/L (120 mg/dL) (strict control), whereas in 69 the goals were fasting blood glucose level less than 5.55 mmol/L (100 mg/dL) and 1.5‐hour postprandial glucose level less than 7.77 mmol/L (140 mg/dL) (customary control).Results:Infants in the strict control group had a significantly lower rate of hypocalcemia (mean calcium less than 8.0 mg/dL in term infants and less than 7.0 mg/dL in preterm infants) than infants in the customary control group (17.6 versus 31.9%;P< .05). Using logistic regression analysis and after adjusting for the effects of gestational age, asphyxia, and White class on hypocalcemia, the difference between groups remained significant. The lowest infant serum calcium concentration correlated significantly with maternal glycohemoglobin A1concentration at delivery (P= .03), gestational age (P= .0001), and the lowest serum magnesium concentration (P= .0001).Conclusion:Strict management of diabetes in pregnancy is associated with a reduction in the rate of neonatal hypocalcemia.(Obstet Gynecol 1994;83:918‐22)