Objectives: To investigate the prevalence of different primary reasons for endodontic referrals and the clinical symptoms of the referred cases. Materials and Methods: Clinical data of total endodontic treatment cases (1,014 teeth) including endodontic referral cases (224 teeth) between January 1, 2010 and December 31, 2012, at Kangdong Sacred Heart Hospital, were investigated retrospectively. The one major reason for referral, the clinical symptoms, and the resulting treatment procedures of referral cases were recorded. The percentages of clinical symptoms of the endodontic referral cases and the total endodontic treatment cases were compared by ${chi}^2$ test for each symptom. Results: Persistent pain was the most frequent reason for endodontic referral (29.5%), followed by presence of gingival swelling and sinus tract (24.1%), and apical radiolucency (12.9%). Referrals in cases involving endodontic difficulties such as canal calcification, broken instruments, post, perforation, and resorption were less than 5.0%, respectively. The percentages of four major clinical symptoms of pain, apical radiolucency, previous endodontic treatment, and gingival swelling and sinus tract were significantly higher in the endodontic referral cases than those in the total endodontic cases (p = 0.001). Among the included referral cases, 72.8% were treated with nonsurgical endodontic treatment only. Teeth other than the referred teeth were diagnosed as the origin of the problem in 5.8% of the referrals. Conclusions: The high prevalence of pain, apical radiolucency, previous treatment, and gingival swelling and sinus tract in endodontic referral cases suggest that these symptoms may be what general practitioners consider to be difficult and refer to endodontists.