Background: In a recent article, Hallinger (2011b) reviewed 135 empirical studies that had employed the Principal Instructional Management Rating Scale (PIMRS) over the prior three decades. The author concluded that the PIMRS appeared to have attained a consistent record of yielding reliable and valid data on principal instructional leadership. However, given the focus of the review, little detail was provided on measurement results related to the PIMRS instrument. Research Design: In light of the extensive past and current use of the PIMRS, the current article seeks to provide a comprehensive and detailed picture of reliability results. More specifically, the authors present a meta-analysis of reliability results derived from 52 data sets derived from 43 independent empirical studies in which the PIMRS had been employed for data collection. Conclusions: The main contribution of this article lies in elaborating on and updating information regarding the measurement properties of the PIMRS, among the most widely used scales in the study and assessment of principal leadership. This information will be useful for researchers who are planning empirical studies of leadership and learning as well as practitioners who have a need for reliable measures of principal instructional leadership. (Contains 6 tables, 2 figures and 13 notes.)