Does the reason why women have no children matter with regard to level of childlessness concerns? Reasons include biomedical barriers, situational barriers, delaying motherhood, and choosing to be childfree. The concept of "childlessness concerns" captures the idea that holidays and family gatherings are difficult because of not having children or feeling left out or sad that others have children. Life course and identity theories guided the structural equation model analyses of a representative sample of 1,180 U.S. women without children from the National Survey of Fertility Barriers. The results indicated that women with the least control over pregnancy, those with biomedical barriers, had the highest childlessness concerns. As hypothesized, the association between reasons and childlessness concerns was mediated by the identity-relevant measure, importance of motherhood. Contrary to the authors' hypothesis, the association was not mediated by social messages to have children. Thus, it is primarily involuntarily childless women who have high childlessness concerns. (Contains 3 tables and 1 figure.)