Mothers of children with developmental delays may experience poorer psychological well-being than other mothers; however, little research has examined how delayed development in children might predict mothers’ perceived physical well-being. Children with delayed development manifest heightened behavior problems, which may negatively affect maternal well-being. We examined the associations between developmental delay and behavior problems at child age 3 and mothers’ self-perceived physical health at child ages 3, 4, and 5, in families of 218 children with and without developmental delays. The study sample comprised 218 families from central Pennsylvania and Southern California, USA who were recruited through community agencies that provide diagnostic and intervention services for individuals with development difficulties. We found that mothers of children with delayed development at age 3 reported poorer concurrent and later physical health than mothers of children with typical development. Broadening the analyses to include not only child development status (delayed development versus typical development) but also child behavior problems at age 3, only child behavior problems and the interaction of development status and behavior problems, but not development status itself, predicted maternal health. Early child behavior problems contributed to later maternal health above and beyond early maternal health, suggesting a possible causal association between child behavior problems and mothers’ physical health. The relation between child behavior problems and maternal health was moderated by mothers’ parenting stress and mediated by depressive symptoms. Mothers of children with both delayed development and high behavior problems are a particular risk group that may be especially in need of early intervention. Further research should examine the behavioral and biological pathways by which these child-related stressors influence mothers’ physical health.