This exploratory study examined perceived sibling compatibility and the effects of personality factors on 134 sibling pairs of older adolescents. The sibling pairs completed an Internet-based survey with a demographic questionnaire and two measures. The Lifespan Sibling Relationship Scale (LSRS; Riggio, 2000) measured perceived sibling compatibility, and the Inventory of Childrens Individual Differences (ICID; Halverson & Havill, et al., 2003) measured personality structure. Results showed that high compatibility sibling pairs were more likely to share in the same levels of certain personality factors and that Agreeableness was most important when predicting perceived sibling compatibility.