A cross-sectional and comparative research design with convenience sampling was used to recruit pregnant women from prenatal clinics in southern Taiwan between 2002 and 2003 to examine the differences in perceived stress, social support, and maternal psychosocial adaptation among women with different severities (mild or less than mild, moderate, and severe) of nausea and vomiting during pregnancy. A total of 150 pregnant women participated in this study. One-way analysis of variance indicated that perceived stress was significantly different among the 3 groups. The least significant difference post-hoc test revealed that pregnant women with mild nausea and vomiting had significantly lower stress than did pregnant women with severe nausea and vomiting. The severity of nausea and vomiting was significantly associated with the Prenatal Self Evaluation Questionnaire subscales for “acceptance of pregnancy” and “fear of helplessness and loss of control in labor.” Social support and maternal psychosocial adaptation were not significantly different among these three groups. The degree of perceived stress and maternal psychosocial adaptation may be related to the severity of nausea and vomiting during pregnancy.