Background/Aims: Excessive gestational weight gain was known to be associated with adverse pregnancy outcomes. It increased the complications during pregnancy, delivery and postpartum period. Nevertheless, there are studies reporting the incompliance of pregnant women with recommendations of weight gain. The objectives of this study were to estimate the prevalence of high gestational weight gain and to identify the increased adverse pregnancy outcomes in these women. Methods: This was a cross sectional study. Data were collected retrospectively from hospital electronic database of Lampang Regional Hospital (LPH) along with manual retrieval from medical charts and labor records. Data of all pregnant women who delivered at labor room of LPH were collected from 1st February 2011 to 31st August 2012. After preterm and multifetal pregnancies were excluded, 4747 cases were brought to the study. This study used the new weight gain recommendation from the Institute of Medicine and National Research Council to classify pregnant women by pre-pregnancy body mass index. Data were analyzed by univariate and multivariate analysis. Results: The proportions of pregnant women with different level of weight gain were 28.4%, 38.5% and 33.1% for low, normal and high weight gain. After multivariate analysis was done to control the confounders, women with high weight gain were significantly correlated with having preeclampsia, higher birth weight group, cesarean section and long neonatal length with relative risk (RR) and 95% confidence interval (95% CI) of 4.84 (2.31 - 10.16), 3.94 (3.24 - 4.79), 2.12 (1.82 - 2.47) and 2.33 (1.90 - 2.86). Conclusions: There were more than half of pregnant women that were prone to have inappropriate weight gain. Many complications from high weight gain that have been reported from aboard also occurred in Thai pregnant women. This should alert corresponding health institute to establish a new guideline to avoid high gestational weight gain.