Background <p>Osteochondral lesions of the talus (OLTs) are a significant cause of chronic ankle pain and functional impairment. However, the relationship between lesion morphology and functional scores remains insufficiently studied, particularly in untreated patients who did not undergo surgical intervention. This cross-sectional study investigates the relationship between MRI-based lesion morphology and functional scores in patients with osteochondral lesions of the talus who did not undergo surgery.</p> Methods <p>This retrospective study included 182 patients diagnosed with OLT based on ankle MRI between January 2023 and March 2025. Lesion surface area and depth were measured using standardized imaging protocols. Functional scores were evaluated using the American Orthopaedic Foot and Ankle Society (AOFAS) score and the Foot and Ankle Disability Index (FADI). Lesions were categorized into six anatomic regions. Demographic variables and lesion characteristics were analyzed for their associations with lower functional scores.</p> Results <p>Medial lesions accounted for 76.3% of cases, with the centromedial region being the most frequently affected (55%). Lesion location did not significantly influence functional scores. In contrast, lesion surface area demonstrated a strong negative correlation with both AOFAS (ρ = − 0.81) and FADI scores (ρ = − 0.81), while lesion depth showed a moderate negative correlation. Age was negatively associated with functional scores. Body mass index and sex did not demonstrate consistent associations.</p> Conclusion <p>These findings indicate that lesion surface area is a stronger predictor of functional impairment than lesion location or depth in the untreated state of non-surgically treated OLT. The results underscore the value of quantitative lesion assessment in the nonsurgical management of talus osteochondral defects and suggest that MRI-based lesion area measurements may help to characterize functional impairment in patients with untreated OLT.</p>