Objective:To determine the correlation between the radiologic magnetic resonance imaging(MRI)depth of invasion(MRI-DOI)and pathologic depth of invasion(p-DOI)in oral cavity primary tongue squamous cell carcinoma(TSCC).Methods:Fifty-two cases of patho-logically proven primary TSCC were selected from patients admitted to The Ninth People's Hospital Affiliated to Shanghai Jiao Tong Uni-versity School of Medicine between January 2015 and December 2018.The p-DOI was measured,and the relationship between p-DOI and patients'clinicopathological parameters and prognosis were analyzed.The MRI-DOI was retrospectively measured,and the correlation between MRI-DOI and p-DOI was investigated.Results:Among the 52 patients,the average p-DOI was(8.5±5.5)(1-30)mm.p-DOI was signi-ficantly correlated with tumor size(P=0.021)and tumor site(P=0.047)when p-DOI was>5 mm,and significantly correlated with level Ⅲ lymph node metastasis(P=0.01)when p-DOI was≥10 mm.A close relationship between p-DOI>7 mm and the patient 5-year survival was also demonstrated(P=0.048).The average MRI-DOI was(10.3±4.3)mm,with a maximum of 19.9 mm and a minimum of 3.1 mm.The MRI-DOI≥10 mm also predicted poor survival in patients with TSCC(P=0.043).The MRI-DOI measured was generally slightly higher than p-DOI,with an average difference of 1.94 mm,and a strong correlation was found between MRI-DOI and p-DOI(r=0.831,P<0.001).Conclusions:MRI-based radiologic DOI measurement was useful in estimating postoperative p-DOI,and may help predict the depth of invasion of tumors preoperatively,which has important reference value for treating primary TSCC.