Objective: Unhealthy weight is a major global health concern. This study examines unhealthy weight among children in Spain and the role of the home environment therein. Data are from a 2010 national survey of families with children. We examined unhealthy weight among children ages 5-10 years using the WHO Child Growth Standards and used multivariate logistic regression to assess associations with family characteristics. Results: There was a high prevalence of unhealthy weight, with only 46% of children at normal weight. Both underweight and obesity were higher among boys (14%; 22%) than girls (13%; 12%). Underweight and obesity were higher among children of mothers with obesity and those with unemployed parents. Obesity was higher among children of mothers who were less educated (35%) and among children of immigrants (19%). We find high levels of unhealthy weight in children, with both underweight and obesity being predicted by the same family environment characteristics.