Clinical perfectionism is characterized by imposing excessively high standards on oneself and experiencing severe distress when standards are not met. It has been found to contribute to the development and maintenance of various clinical presentations including anxiety, obsessive-compulsive, and eating disorders. The present study tested the efficacy of ten weekly individual sessions of acceptance and commitment therapy (ACT) relative to a waitlist control on clinical perfectionism and global outcomes among 53 individuals with clinical perfectionism. ACT is a process-based therapy that targets maladaptive underlying processes (e.g., rigid adherence to unrealistic high standards) rather than symptom topography (e.g., anxiety, depression). Participants completed assessments at pretreatment, posttreatment, and one-month follow-up. Results indicated compared to the waitlist condition, the ACT condition led to greater improvements in clinical perfectionism as well as outcomes related to wellbeing, functional impairment, distress, and processes of change. Our study suggests targeting core dysfunctional processes (i.e., clinical perfectionism) rather than symptom topography with treatments like ACT is feasible and efficacious, supporting a shift from symptom-focused to process-based care. We also note potential weaknesses in our treatment protocol and study methodology that should be addressed in future research. Study limitations included a small sample size and high dropout rate (35.7%).