The relationship between pregnancy-induced hypertension (and pre-eclampsia) and gestational glucose intolerance was examined prospectively in 81 women with gestational diabetes mellitus. A borderline group consisted of 203 women with a single abnormal value on an oral glucose tolerance test. Controls consisted of 327 healthy women with normal glucose tolerance test at 28-32 weeks of gestation. The women with gestational diabetes were older (p < 0.01) and their prepregnancy weight and body mass index were higher (p < 0.001) than those in the control group. Also the women in the borderline group had higher prepregnancy weight (p < 0.01) and body mass index (p < 0.001) than the women in the control group. However, the pregnancy weight gain was lower in the gestational diabetics than in the control women (p < 0.001). Birth weight, birth trauma, low Apgar scores and hypoglycemia did not differ between the groups. However, hyperbilirubinemia occurred more frequently (28.4% vs. 3.7%, p < 0.001) in the gestational diabetics than in the controls. The frequency of both chronic hypertension (2.5% vs. 0.3%, p < 0.05) and pregnancy induced hypertension and pre-eclampsia (19.8% vs. 6.1%, p < 0.001) were higher in the gestational diabetes group, but not in the borderline group when compared with the controls.