The ethnic identity development plays a crucial role in adolescence and emerging adulthood and may be more complex for adoptees who do not share their ethnic identity with their adoptive families. Evidence from the studies was mixed, with strong ethnic identity not always found to be indicative of improved psychological adjustment. Recently research carried out on ethnic minorities has highlighted that the relation between ethnic identity and well-being could be influenced by Bicultural Identity Integration (BII) (Benet-Martínez et al., 2002): It reflects how individuals who experience more than one culture organize and combine their dual cultural backgrounds. These results are consistent also among adoptees (Manzi, Ferrari, Rosnati, & Benet-Martínez, 2013) but need to be further explored. A longitudinal study was conducted to investigate whether and the extent to which ethnic identity, national identity, and BII are protective factors for adoptees' psychological well-being. A self-report questionnaire was administered to 79 Italian transracial adoptees, aged between 15 and 25, at two time points, one year apart. In line with predictions, longitudinal analyses showed the crucial role of BII that turned out to increase higher levels of well-being one year later. Results are discussed in relation to implications for intervention with adoptive parents and children.