Perfectionism can be problematic when your self-worth is dependent on achievements and leads to inflexible standards, cognitive biases, and rigid behaviors. Cognitive behavior therapy for perfectionism is shown to be effective, including for targeting psychiatric symptoms and when delivered via the Internet (iCBT-P). However, few studies have compared it to an active comparator. The current study randomly assigned 138 participants seeking help for perfectionism to iCBT-P or Internet-based Unified Protocol (iUP). Both treatments provided guidance on demand from a therapist and were eight weeks in duration. The results indicated large within-group effects of Cohen's d 2.03 (iCBT) and 2.51 (iUP) on the Clinical Perfectionism Questionnaire at post-treatment, and maintained effects at 6- and 12-month follow-up, but no between-group difference (β = 0.02, SE = 1.04, p = .98). Secondary outcomes of depression, anxiety, quality of life, self-compassion, procrastination, and stress ranged from small to large, with no differences between the conditions. Both treatments were deemed credible, relevant, of high quality, and well-adhered by the participants. Further research needs to be conducted, but the findings could indicate a lack of specificity, perhaps suggesting there is no need to differentiate between different treatments that are transdiagnostic in nature.