A retrospective study. Anterior cervical fusion surgery is widely used procedure in cervical spondylosis. When considering the blood reinfusion strategies of cervical fusion surgery, the amount of blood loss is one of the key elements. We usually calculate the blood loss according to the surgical bleeding plus the postoperative drainage; however, this method ignores the possibility that there may be hidden blood loss (HBL). We performed a retrospective study to determine the risk factors for HBL in patients who underwent anterior cervical fusion surgery for degenerative spine from 2013 to 2016. The Pearson correlation, Spearman correlation, and multivariate liner analysis were used to find association between patient characteristics and HBL. A total of 107 consecutive patients who underwent anterior cervical fusion surgery for degenerative spine in our hospital were reviewed. The amount of HBL was 261 mL, or 50% of the total blood loss. According to the model of multiple linear regression analysis, patient sex (P = 0.028) and American Society of Anesthesiologists physical status classification (P = 0.029) were independent risk factors contributing to HBL, but preoperative hematocrit was not (P = 0.741). We concluded that sex and American Society of Anesthesiologists physical status classification were independent risk factors of HBL in anterior cervical fusion surgery. In addition, there was a high proportion of HBL in anterior cervical fusion. When considering the strategies of transfusion, we should pay attention to the risk factors for HBL. Copyright © 2017 Elsevier Inc. All rights reserved.