To evaluate the effectiveness and safety of physical exercise in terms of maternal/perinatal outcomes and the perception of quality of life (QoL) in pregnant obese and overweight women. A randomised controlled clinical trial. The Prenatal Outpatient Clinic of the Women's Integral Healthcare Centre (CAISM-UNICAMP) at the University of Campinas, Campinas, Brazil. Eighty-two pregnant women (age ≥ 18 years; pre-gestational body mass index ≥ 26 kg/m(2) ; gestational age 14-24 weeks). Women were randomised into two groups: women in one group exercised under supervision and received home exercise counselling (the 'study group'; n = 40) and women in the other group followed the routine prenatal care programme (the 'control group'; n = 42). Primary outcomes were gestational weight gain during the programme and excessive maternal weight gain. Secondary outcomes were increased arterial blood pressure, perinatal outcomes and QoL (WHOQOL-BREF). In the study group, 47% of pregnant women had weight gains above the recommended limit, compared with 57% of women in the control group (P = 0.43). There was no difference in gestational weight gain between the groups. Overweight pregnant women who exercised gained less weight during the entire pregnancy (10.0 ± 1.7 kg versus 16.4 ± 3.9 kg, respectively; P = 0.001) and after entry into the study (5.9 ± 4.3 kg versus 11.9 ± 1.5 kg, respectively; P = 0.021) compared with women in the control group. Arterial blood pressure was similar between the groups over time. There was no difference in perinatal outcome or QoL. The exercise programme was not associated with control of gestational weight gain in our sample as a whole, but was beneficial for lower gestational weight gain in overweight women. Exercise was not associated with adverse perinatal outcomes and did not affect variation in arterial blood pressure or the perception of QoL. © 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2011 RCOG.