Objectives: To identify post-treatment prognostic factors for medication-related osteonecrosis of the jaw (MRONJ). Materials and Methods: We evaluated 54 MRONJ patients who visited the Department of Dentistry, Ajou University Hospital, from May 2007 to March 2014. Twenty-one patients were surgically managed with debridement or sequestrectomy and 33 patients were conservatively managed using antibiotics. Correlations of age, sex, stage, bisphosphonate duration and type, and drug holiday with the prognosis of MRONJ were investigated. Correlations were verified by logistic regression analysis and t-tests with a significance level of 0.05. Results: Clinical outcomes were evaluated on the basis of both clinical and radiographic findings. Twelve out of 21 surgically managed patients showed a favorable prognosis and nine patients relapsed. Thirty-one of the 33 conservatively managed patients showed no specific change in prognosis, and two patients worsened. Statistical analyses of the conservative management group did not reveal any correlation of the above factors with the prognosis of conservative management. Drug holiday was the only prognostic factor in the surgical management group (P=0.031 in logistic regression analysis, P=0.004 in t-test). Conclusion: Drug holiday is a prognostic factor in the surgical management of MRONJ. Because the drug holiday in the patients of the poor prognosis group occurred 1.5 to 4 months prior to surgical management, we recommend a drug holiday more than 4 months before surgery.