For some women, pregnancy may increase the risk of future obesity with consequences for health and well-being. Psychosocial factors may be partly responsible for this. The aim of this study was to examine the association between psychosocial factors during pregnancy and postpartum weight retention (PPWR) at 6 and 18 months. A total of 37,127 women in The Danish National Birth Cohort (DNBC; 1996-2002) participated in four telephone interviews before and after delivery. They gave information about their experience of distress, depression and anxiety, social support, and psychosocial burdens during pregnancy. PPWR was defined as retention ≥ 5 kg at 6 and 18 months postpartum according to a woman's prepregnancy weight. The associations were examined by use of logistic regression and presented as odds radios with 95% confidence intervals. Women who were more likely to feel depressed/anxious or distressed during pregnancy had a higher risk of PPWR at 6 months (1.35 (1.27; 1.44) and 1.30 (1.22; 1.38)) and 18 months (1.34 (1.24; 1.45) and 1.32 (1.23; 1.42)). Likewise, women who felt burdened by their economy or working situation had a higher risk of PPWR as did women with the lowest incomes or less education. Women who reported a high level of distress or depression/anxiety both during pregnancy and in the first 6 months of motherhood had the highest risk of PPWR 18 months postpartum (1.54 (1.39; 1.71) and 1.49 (1.32; 1.69), respectively). Feeling distressed, depressed, or anxious during pregnancy was associated with higher PPWR as was personal and economical burdens. Adverse psychosocial characteristics may be a common determinant of weight retention after childbirth.