The prevalence of childhood overweight is high in Mexican immigrant communities in the United States. Understanding mother's perceptions of child weight in immigrants' country of origin may help to understand this high prevalence. The goal of this study was to examine and compare mothers' perception of weight in Mexico (MX) and in an immigrant community in California (CA). We assessed perceptions of child weight using a pictorial scale with 314 mothers of 5-year-old children in MX and 60 mothers of 5 year-old-children in CA. We compared maternal reports with children's objectively measured weight. Using chi-square Andanalysis of Variance, we investigated associations of maternal perception of and satisfaction with weight according to socio-demographic characteristics. Mothers were more likely to underestimate their children's weight in CA than in MX. On average, CA mothers wanted their children to be smaller than they currently were and mothers in MX wanted their children to be bigger than they currently were. This differed by weight status in CA with mothers of normal weight Andat-risk-foroverweight children wanting them to be bigger and mothersof overweight children wanting them to be smaller. In order for programs to be effective, mothers must be able to recognize their children as overweight and want to address it. Because underestimation of weight Anda desire for a larger size is common in this population, programs to address overweight may be more effective if they focus on alternative benefits of weight control strategies, such as healthy child development. © The Author(s) 2009.