Introduction. Gestational diabetes mellitus (GDM) is defined as glucose intolerance with an onset or first recognition during pregnancy. Previous GDM predisposes the woman to prediabetes or overt diabetes later in life. Lactation seems to have a protective impact on metabolic profile of the women with previous GDM but the results of available studies are conflicting. The aim of our study was to prospectively investigate in a 18-month observation whether lactation duration and intensity influences glucose and insulin response among women with prior GDM, diagnosed according to WHO criteria. Material and methods. The study population consisted of 144 white caucasian women that were initially included in the study. During enrollment visit, between 26th and 30th week of gestation, maternal medical history, the result of 75 g oral glucose tolerance test (75 g OGTT), and anthropometric parameters were collected. Blood samples were collected for additional tests. Final analysis comprised 68 subjects (47.2%) that participated in the follow-up visit 18 months after delivery. Data on delivery and lactation as well as anthropometric data were gathered and 75 g OGTT was performed. The participants were then compared according to lactation duration [longer (> 12 weeks) or shorter (£ 12 weeks)] or lactation intensity [more intensively (> 70% of the total infant milk consumption coming from breastfeeding) or less intensively (< 70% of the total infant milk consumption coming from breastfeeding)]. Results. 53 (78%) women breastfed more than 12 weeks, and 52 (76%) had intensive lactation. The women lactating longer than 12 weeks had significantly higher body weight (p = 0.038) and BMI (p = 0.001) than the women lactating for a shorter period of time. There was a 3-fold higher number of women treated with insulin in the group lactating for a longer period of time (p = 0.038). The women lactating more intensively had significantly lower HOMA 2 IR (p = 0.019) compared to the women breastfeeding less intensively. They had also lower HOMA 2 %B (p = 0.05). The number of subjects with isolated impaired glucose tolerance was significantly higher in the women lactating less intensively (18.7% vs. 1.9%, p = 0.037). A significant negative correlation between lactation duration and fasting glucose concentration (r = –0.282, p < 0.05) as well as fasting insulin concentration (r = –0.251, p < 0.05) was detected. Similar correlation was noticed as concerns 2-h post-load insulin concentration (p = 0.05). Moreover, a significant negative correlation between lactation intensity and fasting insulin concentration (r = –0.251, p < 0.05) was found. In multiple regression model analysis, prepregnancy BMI and gestational weight gain appeared to be the strongest factors influencing the obtained results. Neither lactation duration nor intensity appeared as the significant factors in the model. Conclusions. Our data provide evidence that lactation may have favorable effects on insulin and glucose response after delivery among women with prior GDM who are at high future cardiometabolic risk. The effects seems to be more evident with longer lactation duration as well as higher lactation intensity.