During adolescence, identity development reaches its crucial point. Siblings foster the search for their own uniqueness through social comparisons. These comparisons can lead to identification ("I am like you." or "We are special.") as well as deidentification ("I am different from you!"). In this study, 204 siblings were interviewed to determine in which aspects/traits twins and nontwins perceive similarities and differences between them and their siblings. The number of similarities and differences mentioned was also examined as well as the frequency with which upward, downward, and neutral comparisons are used. It was assumed that monozygotic twins in particular differ from other twins (dizygotic twins of the same and opposite sex) and nontwins (siblings with a maximum age difference of 24 months) due to different developmental conditions. For all siblings, results show that the areas in which similarities and differences are perceived differ. Similarities are mainly perceived in interests and shared abilities/activities, whereas differences are mainly described with the help of character traits, looks, and athletic abilities. Monozygotic twins perceive fewer differences between them than do the other groups but do not perceive more similarities. Twins and nontwins do not differ in the frequency with which upward, downward, and neutral comparisons are used. Implications of these results are being critically discussed. (Contains 1 figure, 4 tables and 1 note.)