To systematically review the proportion of parents able to recognize overweight status in their children who were recorded as being overweight by internationally recognized standards. Two independent reviewers searched electronic databases including MEDLINE, EMBASE, PSYCHINFO, and CINAHL for studies from inception to August 2007 using search terms related to childhood overweight and parents. Twenty-three studies satisfied inclusion criteria, representing 3864 overweight children from 7 countries and 5 distinct standard definitions of overweight status. Seventeen of 23 studies employed either greater than 95th centile or the International Obesity Task Force criteria. Parental recognition of their child's overweight status ranged from 6.2% to 73%, but in 19 of 23 studies, it was less than 50%. More than half of parents cannot recognize when their child is overweight. Relying on parents to seek help for their overweight children is likely to be ineffective, and hence population-based screening may be justified.