Studies on the effectiveness of correctional treatment have widely failed to assess program integrity. This study examined the program integrity of EQUIP in 34 treatment groups of incarcerated offenders, using a new multiaspect program integrity instrument (MIPIE). The first aim of our study was to assess the reliability and validity of the MIPIE. The second aim was to describe the practical application of the instrument as an integrity feedback tool. Results showed that a two-factor solution for the MIPIE appeared to be the most adequate and that the composite program integrity scale of the first factor had a good internal consistency. The interobserver agreement was high. Furthermore, moderate to high relationships were found between observers and trainers, but trainers reported significantly higher program integrity levels. EQUIP was implemented with diverse integrity levels, with higher levels for the United States and program developer sites. By using the MIPIE, detailed feedback can be provided to improve program implementation.