Summary Hypertension in pregnancy is one of the reasons of high rate of perinatal risk. In case of women with high BMI, the rate of hypertension is higher than in pregnant women with normal BMI. The etiology and the role of the environmental factors remain unknown. Aim: The main aim of the study was to assess the influence of high BMI before pregnancy on the risk of hypertension in pregnancy and body mass gain in pregnancy and the frequency of hypertension. Material and methods: The study was conducted in 2005-2007 in 126 women treated in High Risk Pregnancy Medical University Lodz. The study group consisted of 33 pregnant women with hypertension and normal weight and 35 hypertensive obese women. Control groups constituted 27 pregnant normal weight and normotensive women and 31 obese normotensive pregnant women. Prepregnancy body mass index, body mass gain in pregnancy and frequency of hypertension were estimated. Results: Mean value of BMI before pregnancy and in III trimester of pregnancy in pregnant women with normal BMI did not differ in study and control group. In pregnant obese women the rate of hypertension was higher in case of higher BMI. The body mass gain during pregnancy in normal weight women is higher in the group where hypertension occurs, if compared with normotensive women. Conclusion: The risk factor of hypertension for normal weight women is a high body mass gain during pregnancy. In obese women the risk of hypertension in pregnancy is high but not correlated with body mass gain during pregnancy.