Studies show that children with a military parent are at heightened risk of the development of behavior problems. However, there is limited work examining how other factors experienced by military families may also influence behavior problems. In the current study, we recruited three types of Canadian families with a preschooler: families with a deployed military member, families with a nondeployed military member, and nonmilitary families. We examined whether the nonmilitary parent's (in all cases the mother) parenting stress and attachment relationship with the child are associated with behavior problems, and whether deployment status further contributes to the prediction. Child-mother dyads participated in an observed attachment assessment, and mothers reported on their stress levels and their child's behavior. Results showed that both child attachment insecurity and parenting stress were associated with elevated levels of internalizing problems; however, only parenting stress was associated with conduct problems. Military deployment predicted higher levels of internalizing and conduct problems beyond the contributions of attachment and stress. Furthermore, having a father in the military (whether deployed or not) also contributed to internalizing problems. These findings shed light on how the military lifestyle impacts early childhood mental health through the complex interplay between various parts of their environment. K E Y W O R D S attachment, behavior problems, deployment, military, parenting stress 1 PREDICTION OF CHILD BEHAVIOR PROBLEMS Global conflicts such as the recent one in Afghanistan have contributed to an increase in the military deployment of Canadian Armed Forces personnel during the past few decades. Given the challenges that a long-term separation from a parent brings forward, scholars have been preoccupied with the potential detrimental effects of military deployment on children. Notably, they found that parental deployment may be a threat to early childhood mental health, notably by increasing the prevalence of internalizing and externalizing problems (Moeller, Culler, Hamilton, Aronson, & Perkins, 2015). However, past research neglected to consider whether deployment in itself predicts behavioral problems, or if other changes related to deployment (e.g., changes experienced by the at-home parent; Flittner O'Grady, Whiteman, Cardin, & MacDermid Wadsworth, 2018) may explain the higher prevalence of behavioral problems among children with a deployed parent. In the current study, we sought to address