Using a retrospective survey design, adults who were raised with a chronically ill sibling were asked to report on levels of parentification, differential parenting, and communication/disclosure of the chronic illness during childhood and adolescence as well as the quality of their sibling relationship during childhood. Participants (N=107) were recruited via Amazon’s Mechanical Turk (MTurk) and reported having a sibling with one of the following chronic illnesses: Cystic Fibrosis, Sickle-Cell Disease, Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, or Hemophilia. A multiple regression examined whether sibling relationship scores could be predicted from sibling differential experiences with mother (Model 1a) and sibling differential experiences with father (Model 1b), with communication scores as a moderator. Results indicated that communication scores significantly predicted sibling relationship scores (p < 0.05) within both Model 1a and 1b. Additionally, sibling differential experiences with their father (p = 0.0241), but not mother (p = 0.3273), predicted sibling relationship scores. A multiple regression was performed to evaluate the degree to which sibling relationship scores could be predicted from parentification scores, with communication scores as a moderator (Model 2). Data analyses found that parentification scores were not predictive of sibling relationship scores. Communication scores significantly predicted relationship scores (p < 0.05), but the interaction (parentification score x communication score) was only marginally significant (p = 0.0655). These findings indicate that communication/disclosure of the chronic illness to the healthy sibling has important implications on the quality of the sibling relationship.