The aim of this study was to investigate the relationship between self-differentiating perceptions and the separation-individuation process in adolescent twins compared to non-twin siblings. A group of 32 twins aged 12-20 years, and a group of 31 non-twin adolescents aged 12-19 years were evaluated using a socio-demographic and clinical information form, the Sibling Inventory of Differential Experience (SIDE) and the Separation-Individuation Test of Adolescence (SITA). There were no significant differences between the twin and the non-twin adolescents with respect to mean scores of SIDE and SITA subscales. Although there were significant differences in the relation of differential peer characteristics to separation-individuation process in two groups, differential experiences of twins related to interactions with their co-twins, mothers' and fathers' affection and controlling behaviors were much more correlated with healthier separation-individuation in adolescence compared to non-twin adolescents. The above-mentioned aspects of self-differentiating perceptions of twins will be important in helping them during the process of separation-individuation.