Background: To date, there have been no studies in Poland on weight gain in women with twin pregnancies in relation to recommendations. Objective: The aim of this study was to analyze the gestational weight gain of women with twin pregnancies depending on their body weight before pregnancy, and to assess the relationship between the observed weight gain and the neonatal birth weight. Material and Methods: The study was conducted among 50 women in twin pregnancies and their 100 newborns delivered after 36 weeks of gestation. Gestational weight gain was assessed based on the American Institute of Medicine guidelines for women in twin pregnancies. Data on the pre-pregnancy body weight and gestational weight gain were collected by interviewing the patients. Neonatal data were obtained from the hospital medical records. Results: Normal gestational weight gain was observed only in 38% of the women. In women with monochorionic pregnancy, too low body weight gain occurred almost 3 times more often than in women with dichorionic pregnancy (74% vs. 26%), (p<0.001). Women with monochorionic pregnancies also gave birth to statistically significantly more newborns with low birth weight (<2500 g), compared to women with dichorionic pregnancies (62.5% vs. 37.5%) (p=0.007). The mean birth weight of newborns born to mothers with excessive weight gain was 151 g higher than children born to mothers with normal weight gain (2727 g vs. 2576 g) (p=0.035). Conclusions: In the majority of studied women in twin pregnancies, gestational weight gain was not compliant with the current recommendations. The risk of insufficient weight gain is higher in women with monochorionic pregnancies compared to women with dichorionic pregnancies.