Parental depressive symptoms are associated with greater variability and inconsistency in parenting behavior as well as children's emotional and behavioral dysregulation. The present study whether such relations extended to dyadic processes, examining whether maternal and paternal depressive symptoms at child age 3 ½ interacted with concurrent higher dyadic behavioral variability (DBV) in mother-child free play to heighten children's emotional and behavioral dysregulation at age 4 (N = 100). Child dysregulation was measured as mother- reported emotional lability/negativity and externalizing problems and DBV was measured as the number of transitions among dyadic behavioral states using State Space Grids. Parent behaviors included parent directives, positive reinforcement, and disengagement and child behaviors included child compliance, persistence, and noncompliance, among others. Analyses also accounted for the degree of positive (as compared to negative) behavioral content. Moderation analyses showed that DBV predicted greater child dysregulation only when maternal or paternal depressive symptoms were higher. Further, DBV was detrimental only when dyadic positive interaction content was low. Findings suggest dyadic behavioral variability combined with low positive content in parent-child interactions is a particular risk factor for children's regulatory development. Fostering positive, predictable interaction patterns may be an important target for family interventions with a depressed parent. [This paper was published in "Journal of Family Psychology" v35 n2 p247-257 2020.]