Background: Piriformis syndrome, an often-overlooked cause of sciatica, commonly presents as chronic gluteal pain and poses a diagnostic challenge, particularly in patients with axial spondyloarthritis (axSpA). Purpose: To examine piriformis muscle abnormalities on sacroiliac magnetic resonance imaging (MRI) and their association with clinical outcomes in patients with axSpA. Material and Methods: This cross-sectional study included 100 axSpA patients (50 radiographic [r-axSpA], 50 non-radiographic [nr-axSpA]), classified by the 2009 ASAS Axial Spondyloarthritis criteria, who underwent MRI evaluations of the sacroiliac joints over a 6-month period. Piriformis evaluation included the measurement of muscle size, signal intensity, and the assessment of fatty infiltration. Sciatic neuritis was assessed by identifying enlarged sciatic nerves or increased signal intensity. Data collection included demographic details, disease activity, and functionality parameters. Statistical analysis was performed using appropriate methods, with P < 0.05 indicating significance. Results: Piriformis syndrome findings were identified in 10% of patients, with a slightly higher incidence in r-axSpA patients (12%) compared to nr-axSpA patients (8%); however, this difference was not statistically significant (P = 0.739). Patients with these MRI findings had significantly higher disease activity, as indicated by the Ankylosing Spondylitis Disease Activity Score with C-reactive protein (3.5 vs. 2.82; P = 0.015), and greater functional impairment, measured by the Bath Ankylosing Spondylitis Functional Index (5.45 vs. 2.7; P = 0.041). Conclusion: This study highlights the presence of MRI findings associated with piriformis syndrome among axSpA patients, which are linked to increased disease activity and reduced function. Recognizing piriformis syndrome as a co-morbidity may improve diagnosis and treatment, leading to better patient outcomes.