Co‐rumination refers to the process of engaging in repeated discussion of personal problems in dyadic relationships. The current systematic review and meta‐analysis provided an evaluation of the relationship between co‐rumination and internalizing problems in children, adolescents and young adults, along with an investigation of potential moderator variables. Studies were eligible for inclusion if they quantitatively assessed the relationship between co‐rumination and depression, anxiety and/or internalizing problems using validated measures. An electronic search was conducted in PsycINFO, PsycARTICLES, Medline, Scopus and the Cochrane Library database of systematic reviews for studies published since 2002. In addition, unpublished studies were located by contacting authors in the field and by online searches of dissertation databases. Thirty‐eight studies were deemed eligible for inclusion comprising a total of 12 829 community‐based participants. A random‐effects model was employed in the analysis, and effect sizes were obtained exclusively from cross‐sectional data. Small to moderate effect sizes were found across four outcomes representing internalizing problems (mean corrected correlation range 0.14 to 0.26), with no significant variability across these variables. Female participants were found to score significantly higher on measures of co‐rumination compared with males (d = −0.55). Moderator analyses revealed mixed findings. No significant effects were found for age, gender or publication status. A significant effect was found for co‐rumination questionnaire version used (p = 0.05), and a marginal effect found for co‐rumination partner (same‐sex best friend versus other confidants; p = 0.08). These findings indicate that co‐rumination may have a modest but significant association with internalizing problems. The implications of these findings and directions for further research are discussed. Copyright © 2016 John Wiley & Sons, Ltd. Key Practitioner Message Co‐rumination has maladaptive (repetitive, unproductive discussion of problems) components, but also shows an association with friendship satisfaction. The current review found that co‐rumination has small‐moderate association with depression and anxiety. Practitioners should be aware of the way in which people discuss affective distress with others.