The onset of psychiatric symptoms and disorders is relatively common in childhood, occurring among youths across the weight spectrum. However, available research suggests that certain psychiatric comorbidities are more prevalent in obese children and adolescents than in healthy weight youths. First, we review research on disordered eating, including evidence to suggest that loss of control eating is associated with weight gain and obesity in youths, as well as poor outcome in family-based treatment of paediatric obesity. Second, we highlight evidence on the relationship between depression and obesity, especially in girls. Third, we present data on attention deficit hyperactivity disorder (ADHD), particularly the symptoms of impulsivity and inattention, and childhood obesity. We also consider that some medical conditions and psychotropic medications contribute to weight gain and obesity in children and adolescents. Throughout the review, we emphasize that psychiatric comorbidity may be a cause or consequence of childhood obesity, or they may share common aetiological factors.