Research on the division of paid and unpaid work at the transition to parenthood has rarely been able to separate the social construction of gender and motherhood/fatherhood identities from labour market and financial factors. By bringing in female same-sex couples (SSC) and comparing how the transition to parenthood influences the division of parental leave in SSC and different-sex couples (DSC), we can isolate parents’ gender as a predictor of the division of care from physiological and identity-forming aspects linked to being a birth-mother (or her partner). Analysing Swedish register data for couples who had their first child in 2003–2011, results show that (i) the (birth) mother’s leave uptake is higher than the partner’s uptake for both SSC and DSC, providing support for identity formation and internalized norms linked to the child’s need of its (birth) mother; (ii) birth-mothers in SSC on average take 7 weeks less parental leave than mothers in DSC, indicating that the partner’s gender plays a role; and (iii) the (birth) mother’s parental leave share is negatively related to her income but unrelated to her partner’s income, suggesting that her labour market prospects are more important in the division of leave than any financial, family-utility maximization.