Objective The aim of this meta-analysis was to provide an up-to-date review of the literature to enhance our understanding of how chronic health conditions (CHCs) affect siblings, both positively and negatively. Methods PsycINFO and Medline were systematically searched. Inclusion criteria were as follows: (a) peer-reviewed, empirical research report; (b) sample n ≥ 10; and (c) reports statistics on siblings’ internalizing problems, externalizing problems, and/or positive self-attributes. Results Overall, there was a significant small negative effect of CHCs on siblings (d+ = −.10). Siblings of children with CHCs had more internalizing problems (d+ = .17), more externalizing problems (d+ = .08), and less positive self-attributes (d+ = −.09) than comparisons. Older siblings and siblings of children with life-threatening and/or highly intrusive CHCs were more at risk for psychological problems. Conclusions This study identified several mechanisms through which CHCs affect siblings. Future research should focus on parent–child dynamics and the longitudinal development of positive self-attributes and internalizing problems as well as on identifying what works in services for siblings of children with CHCs.