Previous studies have shown that lesbian and gay (LG) individuals, in comparison to their heterosexual counterparts, tend to report lower levels of parenthood desire. While numerous variables have been suggested to explain this gap in parenthood aspirations, no study has investigated the mediating role of avoidant attachment in the association between sexual orientation and parenthood desire. For that purpose, a sample of 790 cisgender Israelis aged 18–49 years (M = 28.27, SD = 4.76) was recruited using convenience sampling. Among the participants, 345 self-reported as predominantly or exclusively lesbian or gay and 445 self-reported as exclusively heterosexual. Participants completed online questionnaires assessing their sociodemographic characteristics, parenthood desire, and avoidant and anxious attachment styles. Mediation analyses were performed using the PROCESS macro, and the results revealed that LG individuals reported lower parenthood desire, higher avoidant attachment, and higher anxious attachment compared to heterosexual individuals. Moreover, avoidant attachment had a significant mediation effect in the association between sexual orientation and parenthood desire. The findings suggest that LG individuals are more likely to report higher avoidant attachment due to possible rejection and discrimination from family members and peers, and this may be associated with lower parenthood desire. The results contribute to the growing body of research on family formation and parenthood aspirations among LG individuals, and specifically studies aimed at delineating the factors that contribute to the gap in parenthood aspirations between sexual minority individuals and their heterosexual counterparts.