Background Weight stigma is a serious challenge because of its negative impact on human health and harmful psychological and behavioral consequences. The aim of the study was to explore and compare the relationships between self-reported body weight and weight-related stigmatization experiences and body image, mental self-image, self-esteem, and stereotypes concerning people with obesity among young adult Polish women (N = 374; aged between 18 and 35). Methods The study was conducted online on a Polish sample recruited through a social network site, a website, and snowball sampling. Body mass index (BMI) was used to assign the respondents to groups with normal or excess weight. We tested whether women enrolled in the study experienced weight-related stigmatization using two questions based on the concepts of spoiled identity and related to the obesity stigma. The Contour Drawing Rating Scale was used to study different aspects of the body image and discrepancies between them. The Self-Discrepancy Questionnaire was used to study the self-schemas associated with mental qualities. The Polish version of the Rosenberg's Self Esteem Scale was applied to determine self-esteem level. Stereotypes concerning people with obesity were studied using the semantic differential method. Results Although excess weight was associated with weight-related stigmatization experiences, many women reported confronting such stigmatization even though their body weight was normal according to the World Health Organization (WHO) standards. Women with excess weight and women with weight-related stigmatization experiences were characterized by larger discrepancies between the actual body image and the ideal, reflected, and ought body image, lower self-esteem, and more negative beliefs about their mental actual and reflected self compared to women with normal weight and without weight-related stigmatization experiences. The study participants from all groups tended to believe their actual body image to be ampler than the ideal and the ought body images. They also believed that other people perceived their mental qualities more positively than they did. The study groups were also characterized by negative stereotypes of people with obesity, although these stereotypes were more vital in women with excess weight and women who experienced weight-related stigmatization. Conclusion The study shows the similarity between psychological functioning of women with self-reported excess weight and those who experience weight-related stigma. The results also provide guidelines for practical actions aimed at reducing negative mental outcomes associated with not conforming to body weight standards.