The purpose of this study was to empirically investigate a family-centered approach to positive behavior support (PBS) that was designed to be culturally responsive to families of diverse linguistic and cultural backgrounds. A Japanese mother and a child with autism were the primary participants. Multiple research methods were used. A single-subject withdrawal design evaluated the functional relation between parent implementation of a culturally informed PBS plan and improvements in child behavior and participation in a dinner routine. Qualitative case study methods guided an understanding of the family’s culture, the mother’s perspectives on the PBS plan and outcomes, and the interventionist’s perspectives on the provision of behavior support to the family. Quantitative results documented a functional relation between implementation of the PBS plan and improvements in child behavior and participation in the dinner routine. Qualitative results provided a rich description of the parent’s and interventionist’s experience and perspective. Three themes emerged: (a) developing a rapport informed by family culture; (b) working with a cultural guide to facilitate understanding the family’s cultural values, beliefs, and parenting practices; and (c) accommodating the mother’s cross-cultural values and beliefs. Contributions to the literature and implications for behavior interventionists working with families of diverse cultural backgrounds are discussed.