Most cases of ovarian torsion require emergency surgery; the ovary has become necrotic and cannot be conserved. Preoperative determination of the ovarian necrosis extent is difficult but it may increase the likelihood of the ovary conservation. In this study, we retrospectively evaluated the findings in ovarian torsion among patients with ovarian tumors who underwent emergency surgery at a single hospital for possible preoperative indicators of ovarian viability. We thus evaluated 77 patients who were intraoperatively diagnosed with torsion of ovarian tumor between 1995 and 2010. These patients were classified into three groups depending on the postoperative histopathological findings: necrotic, congestive, and normal. Preoperative C-reactive protein (CRP) level, leukocyte count, and body temperature, along with tumor size, degree of torsion, time from the onset of abdominal pain to surgery, and incidence of acute abdomen were compared among the three groups. The sensitivity, specificity, and positive and negative predictive values of the preoperative serum CRP levels for ovarian necrosis were calculated. The CRP level, degree of torsion, and time from the onset of abdominal pain to surgery were significantly higher in the necrotic group than in the normal group. The sensitivity and specificity of the CRP level for necrosis were 35% and 83%, respectively, and positive and negative predictive values were 38% and 82% respectively. The potential for ovary conservation in suspected ovarian torsion should be greater if the tumor is non-malignant, the time from the onset of abdominal pain to operation is short, and the CRP level is < 0.3 mg/dl.