Objectives: The whirlpool sign (WS) and plasma D-dimer are used as a sonographic marker and laboratory index for adnexal torsion (AT), respectively. The aim of this study was to evaluate whether their combination improved diagnostic efficiency of AT in patients presenting with a benign ovarian mass and abdominal pain and clinically suspected AT. Materials and methods: Fifty-four patients with clinically suspected AT with benign ovarian mass and abdominal pain were analyzed and divided into an AT group (n = 28) and control group (n = 26). Ultrasonography and venous blood collection were performed before surgery to observe the WS and plasma D-dimer level. All cases were confirmed by surgery. Diagnostic efficiency of the WS, plasma D-dimer level, and their combination was compared. Results: There was a significant increase in the WS and plasma D-dimer level in AT patients (all p < 0.01). The sensitivity, specificity, Youden Index and area under the curve (AUC) of the WS (cut-off value of > 1 circle), D-dimer level (cut-off value of 248 ng/ml) and their combinations were 71.43, 67.86 and 96.43%; 92.31, 100 and 100%; 0.637, 0.679 and 0.964; and 0.909, 0.899 and 0.995, respectively. There was a significant difference in AUC between the WS and D-dimer and their combination (all p < 0.01). Conclusions: The WS and D-dimer were useful for diagnosis of AT in patients with ovarian mass and abdominal pain. Combination of the WS and D-dimer may improve diagnostic efficiency for AT compared with each method alone.