Objective To explore the value of differential diagnosis of modified Neer impingement sign for subacromial impingement syndrome and frozen shoulder.Methods 115 patients(123 shoulders) with shoulder joint disease were checked by the Neer impingement sign and modified Neer impingement sign,and the sensitivity,specificity,positive predictive value,negative predictive value,and accuracy of the test for subacromial impingement syndrome was observed.Results The diagnostic rate of accuracy of modified Neer impingement sign for subacromial impingement syndrome was 91.06%,and the specificity was 95.51%,while for frozen shoulder the accuracy was 95.93%,and the specificity was 90.09%.Conclusion Modified Neer impingement sign for subacromial impingement syndrome and frozen shoulder has diagnosis accuracy,good reliability,and it is a reliable method for diagnosis of subacromial impingement syndrome and frozen shoulder,and has a good differential diagnostic value for the two diseases. Key words: Should impingement syndrome ; Diagnosis ; Frozen shoulder ; Shoulder jiont