A central issue in adoption research is understanding why some individuals adapt to their adoption experience while others face considerable difficulties. The social identity approach (SIA) offers a valuable framework for examining this. Recent research has increasingly shown that identifying with social groups can protect and promote well-being. However, in the context of adoption, certain groups may also present challenges or become sources of strain. The present study seeks to understand how social identities shape individuals' adoption experiences. Semi-structured interviews (N = 16) with adults who were adopted through Mother and Baby Homes in Ireland were analysed using reflexive thematic analysis. The analysis produced two interrelated themes: (1) 'Adopted' as a social identity, which explores how participants' 'adopted' status itself constitutes a significant social identity, leading to experiences of marginalization and exclusion and (2) Adoption as social identity loss, which describes how participants face contested membership and compromised belonging within important social groups. Both themes illustrate how the process of adoption can result in social identity loss. Discussion of this analysis considers the consequences of social identity change for adoption adjustment. These findings expand the theoretical application of the SIA, in the context of adoption.