Attention-deficit hyperactivity disorder (ADHD) in children and adults increases risk of parenting difficulties and interparental discord. However, little is known about whether disruptive child behavior and adult ADHD operate additively or synergistically to predict parenting and interparental relationship quality. As part of a larger study, 90 parent couples were randomly assigned to interact with a 9–12 year-old confederate child exhibiting either ADHD/ODD-like behavior or typical behavior. Before these interactions, parents reported their own ADHD symptoms. Afterwards, parents reported on their partner’s parenting and interparental communication behavior. Observers coded the parenting and communication behavior of both partners during the tasks. Child ADHD/ODD-like behavior was found to predict less positive and more negative parenting and communication reported by partners and observers beyond adult ADHD symptoms and other covariates. Elevated adult ADHD symptoms only uniquely increased risk of observer-coded negative parenting. Child and adult ADHD behavior interacted synergistically to predict partner-reported negative parenting and interparental communication, such that parents reporting greater ADHD symptoms—especially inattentiveness—were rated by their partners as parenting and communicating more negatively when managing child ADHD/ODD-like behavior than parents with fewer ADHD symptoms or those managing typical child behavior. Child and adult ADHD behavior did not interact to predict observer-coded parenting or interparental communication, and patterns did not differ for mothers or fathers. Our results underscore the potential risk of parents with elevated ADHD symptoms parenting and communicating negatively, at least as perceived by their partners, during interactions with children exhibiting ADHD/ODD behavior.