We examined the occurrence and stability of behavior problems over a 6-year period among 193 adults with mental retardation who lived with their mothers. At the beginning of the study period, almost 30% of the sample had clinically significant behavior problems and about 25% had no behavior problems. During the study period, group-level stability of behavior problems and individual-level change were observed. We tested the bidirectional relations between behavior problems and maternal well-being and found evidence of both directions of influence. Initial levels and changes over time in behavior problems predicted changes in maternal well-being, and initial levels and changes over time in maternal well-being predicted changes in behavior problems in the son or daughter.