Parents of children with developmental disabilities (DD) are at increased risk of experiencing psychological stress compared to other parents. Children’s high levels of internalizing and externalizing problems have been found to contribute to this elevated level of stress. Few studies have considered the reverse direction of effects, however, in families where a child has a DD. The present study investigated transactional relations between child behavior problems and maternal stress within 176 families raising a child with early diagnosed DD. There was evidence of both child-driven and parent-driven effects over the 15-year study period, spanning from early childhood (age 3) to adolescence (age 18), consistent with transactional models of development. Parent–child transactions were found to vary across different life phases and with different domains of behavior problems.