This meta-analysis examines loneliness in children and adolescents with chronic physical conditions as compared with their peers. Multilevel meta-analyses were performed on 43 studies (69 samples), published between 1987 and 2015. A total of 2,518 individuals with chronic physical conditions and 1,463 control peers were included in the analyses. Children and adolescents with chronic conditions are, on average, somewhat lonelier than their peers without such conditions. Moreover, the link between chronic conditions and loneliness varied according to the recruitment procedure used for participant selection. Stronger links were found for studies that recruited from patient organizations as compared with clinical registers. Findings support the link between loneliness and chronic conditions. To take into account the heterogeneity within patient groups, we advocate an alternative approach that cuts across diagnostic boundaries and focuses on illness-related variables such as illness duration and visibility of the condition.