Introduction: The aim is to define whether the measurement of glenoid and Hill-Sachs defects by magnetic resonance imaging is equivalent to the measurement by simple tomography in patients with anterior shoulder instability.Materials and methods: Descriptive, observational, cross-sectional study of a cohort of imaging studies of patients with a history of anterior shoulder dislocation, comprising magnetic resonance and simple tomography of the shoulder, performed in a fourth level hospital.Results: The cohort consisted of 20 cases; a high and statistically significant correlation was found for the measurement of the glenoid diameter and defect, with a p < 0.05 between the MRI and simple tomography. In addition, the Hill-Sachs interval measurement was found to be statistically significant, but the correlation index was not high, 60%. For intraobserver agreement, a Kappa index was calculated for MRI of 0.8 compared to CT with p-value <0.05 significant for engaging and non-engaging defects.Conclusion: Simple MRI is a reliable imaging method with high correlation index for the measurement of diameter and glenoid defects with good agreement to establish whether Hill-Sachs defects are engaging or not.Level of Evidence: Level III