Parent-Child Interaction Therapy (PCIT) has been shown to reduce challenging child behavior and improve parenting skills, yet treatment attrition, non-adherence and non-response remain matters of concern. This study analyzes rates and factors associated with attrition, non-adherence, and non-response using data from a randomized controlled trial of foster parent-child dyads who received brief, group-based PCIT. Multivariate logistic regressions demonstrated that, as compared to prior estimates of conventional outpatient PCIT, rates of treatment attrition, non-adherence and non-response from the group-based PCIT intervention were low. Compared to other racial/ethnic groups, rates of attrition were significantly higher among African American foster parents. No study variables were linked to treatment non-adherence. Foster parent ratings of child externalizing symptoms were positively associated with non-response. Implications for promoting retention and treatment effectiveness, successfully integrating PCIT into child welfare services and advancing future research are discussed.