There is mounting evidence that family functioning is linked to childhood overweight and obesity, and that both of these are associated with health-related behaviours and adverse health outcomes in children and adolescents. This paper systematically examines the peer-reviewed evidence regarding the relationship between child and adolescent overweight and obesity and family functioning. Peer-reviewed literature published between 1990 and 2011 hosted in Scopus, Pub Med or Psyc INFO were searched, in addition to the reference lists of included papers. Twenty-one studies met the selection criteria. Of the 17 identified cross-sectional and longitudinal studies, 12 reported significant associations between family functioning and childhood overweight and obesity. The instruments used to measure family functioning in the identified studies were heterogeneous. Poor family functioning was associated with increased risk of obesity and overweight in children and adolescents, and obese children and adolescents were more likely to come from families with poor family functioning. Aspects of family functioning which were associated with increased risk of child and adolescent obesity included poor communication, poor behaviour control, high levels of family conflict and low family hierarchy values. Half (2/4) of the identified intervention studies showed a significant relationship between family functioning and changes in child weight. The results demonstrate that family functioning is linked to obesity; however, higher level evidence and greater understanding of the mechanisms behind this relationship are required. The results indicate a need for a standardised family functioning measure applicable across populations. The results provide evidence of the value of considering family functioning in childhood obesity research and intervention.