Background: Cognitive fatigability (CF) can be defined as an objective decline in performance that occurs over time during sustained cognitive effort. Previous work has shown that the Paced Auditory Serial Addition Test (PASAT) is a sensitive measure of CF in MS. Although CF is a common and debilitating symptom, there is currently little standard for its quantification making it difficult to apply in a clinical setting. Objectives: The objective of this study was to validate regression-based normative data for the PASAT in an Ontario-based MS sample. Both PASAT performance and cognitive fatigability scores were evaluated. Methods: Healthy controls (HCs) and persons with MS (PwMS) completed the 3 and 2 PASAT. PASAT performance was measured with total correct, dyad, and percent dyad scores. CF scores were calculated by comparing performance on the first half (or third) of the task to the last half (or third). A series of ANCOVAs were performed to compare both performance and CF scores between PwMS and HCs. Chi-square tests compared group differences for the number of persons classified as impaired on each measure. Results: Results showed that PwMS performed worse than HCs across all performance measures, while PwMS only performed worse than HCs on CF measures of the 3 PASAT. All performance measures of the 3 PASAT classified more PwMS as impaired than HCs. Only the total correct score classified more PwMS for the 2 version. More PwMS were classified as impaired on all CF measures for the 3 PASAT compared to HC, though not to a statistically significant degree. Conclusions: Results indicate that, although findings differ based on the interstimulus interval and the scoring methodology, the PASAT is sensitive to group differences in performance. Furthermore, the 3 PASAT is also sensitive to group differences in CF. Performance impairment was observed using regression-based norms, largely on the 3 PASAT, but the ability of the normative data to detect impairment in CF was less clear. This may reflect the unique demographic characteristics of this Ontario-based sample. Future work will evaluate how these regression-based normative results compare to discrete normative data in this sample.