The degree of maternal glucose control achieved during the third trimester of pregnancy was evaluated for 120 overtly diabetic women hospitalized on a high-risk pregnancy ward. "Rigid" blood glucose control, defined as a mean preprandial plasma glucose concentration less than 115 mg/dl was achieved in only 14% of these women. Although mean preprandial plasma glucose concentrations ranged between 115 and 172 mg/dl in 66% of women and exceeded 172 mg/dl in 20%, the perinatal salvage rate was greater than 95%. Pregnancies of those women whose mean plasma glucose levels exceeded 172 mg/dl required earlier intervention for signs of fetal jeopardy, but the degree of glucose control was not significantly related to either perinatal death or neonatal morbidity. These results suggest that maternal hyperglycemia exceeding a mean preprandial glucose concentration of 172 mg/dl is to be avoided, whereas, at the other extreme, mean glucose levels less than 115 mg; dl or "rigid" control is unnecessary for a successful perinatal outcome. © 1979.