- OBJECTIVE: To determine the reliability and correlation of plain radiography and magnetic resonance imaging (MRI) in the assessment of acromion morphology. MATERIALS AND METHODS: Acromion morphology was assessed using the lateral acromion angle (LAA) and the acromion-humeral interval (AHI). Thirty patients who had X-rays and MRI for impingement syndrome were included. Six blinded observers assessed the acromion morphology subjectively and objectively. RESULTS: Neither acromion assessment technique demonstrated a positive correlation (kappa and intraclass coefficient < 0.55) between X-ray and MRI. Both techniques were reliable (kappa and intraclass coefficient > 0.55) when measured objectively by experienced observers. CONCLUSION: The LAA and the AHI are both reliable acromion assessment techniques on X-ray and MRI when measured objectively and by experienced observers.