Introduction: Obesity is a growing global public health problem and is as prevalent among pregnant women as in the general population. It is well known that obese women have an increased risk for several complications during pregnancy and delivery and this is also true for the neonate. Excessive gestational weight gain among obese women seems to further increase these risks for adverse outcomes. It has not been known up to the time of this study whether a behavioral intervention program designed for obese pregnant women could result in a reduction of gestational weight gain. Aim: The overall aim of the present thesis was to study the effect of an intervention program designed to control weight gain among obese pregnant women during pregnancy and to then observe the outcomes of their pregnancies. In addition we wanted to learn if this behavioral intervention program could result in a weight gain of less than seven kilograms. Material and methods: The intervention group consisted of 155 obese (BMI >30 kg/m2) pregnant women at the antenatal care clinic (ANC) in Linköping; the control group consisted of 193 obese pregnant women in two other cities. The women in the intervention group were offered, in addition to regular care at the ANC, motivational interviewing in weekly visits to support them in making this behavioral change. They were also offered aqua aerobic class once or twice a week. The women in the control group attended the routine antenatal program in their respective ANCs. Outcome measures were: weight in kg, pregnancy-, delivery and neonatal outcomes, prevalence of anxiety- and depressive symptoms and attitudes and experiences of participating in an intervention program. Results: The women in the intervention group had a significantly lower gestational weight gain and also had a lower postnatal weight than the women in the control group. The percentage of women in the intervention group who gained <7 kg was greater than the percentage in the control group. There were no differences between the two groups in pregnancy-, delivery- and neonatal outcomes. In addition, there was no difference in prevalence of symptoms of anxiety and depressions between the intervention- and control group and the gestational weight gain did not have any effect on symptoms of depression or anxiety. The women in the intervention group with gestational weight gain <7 kg, weighed less at the two years follow-up than the women in the control group. Most of the women who participated in the intervention program expressed positive attitudes and were positive towards their experiences with the intervention program and their efforts to manage the gestational weight gain. Conclusion: The intervention program was effective in controlling weight gain during pregnan-cy and did not change the pregnancy, delivery or neonatal outcomes or the prevalence of anxie-ty- and depressive symptoms. The group with a gestational weight gain <7 kg showed the same distribution of complications as the group with a higher weight gain. The intervention program seems to influence the development of weight in a positive direction up to two years after childbirth. The women were also satisfied with their participation in the intervention program.