Summary This article examines a case of gay parenting analysed in the context of a collective, interdisciplinary research project funded by the French National Research Agency ( Agence Nationale de la Recherche ). Its authors use a clinical psychoanalytical approach, applying this methodology to the single case study of a lesbian couple and their son, who was eight and half years old at the time of the research project. The clinical data were gathered using several techniques: interviews with the parents and the completion of a family tree, a projective test, and a game with the child. The analysis, drawing on psychoanalytical conceptual frameworks, describes how belonging and difference are both constructed and transmitted along family lines. Data obtained relating to the mothers reveal how the relationship within the couple is articulated with Oedipal configurations, ancestral history and representations of the sperm donor that interact with intrapsychic conflicts and the differences they promote, including those along the lines of gender. Analysis of the data produced with the child suggest that he uses these situations to create a representation of his place within the successive generations in his family, his own gender identity and his fantasies spun out around the identity of the sperm donor.