Background: Accidental hemorrhage is defined as abnormal complete or partial separation of normally implanted placenta after 20 weeks of gestation and prior to birth. Risk factors which have been found associated with accidental hemorrhage include maternal age, parity, smoking, hypertension, past history of accidental hemorrhage, thrombophilic disorders, abdominal trauma and polyhydramnios. Aim of the Work: The aim of our study was to find if there is any role for decidual natural killer cells in cases with placental abruption. Patients and Methods: This is a case control study in which 60 pregnant women recruited from Obstetric Department of Ain Shams University Maternity Hospital. Patients were subjected to emergency cesarean section. Multiple tissue biopsies (5 mm thick) were taken from the decidua basalis of the placental bed and immunostained for decidual CD 56+ve bright natural killer cell marker.  Results: Our results show that there was a highly statistically significant difference between the study and control group as regard immunohistochemical scores (according to CD 56+ %), In control group: score 0 = 0.0%, score 1+ = 0.0%, score 2+ = 18.5%, score 3+ = 29.6%, score 4+ = 51.9% while in the study group: score 0 = 25.9%, score 1+ = 40.7%, score 2+ = 29.6%, score 3+ = 3.7%, score 4+ = 0.0%; (Chi square 42.133 FE) and (P. value = 0.000). Also there was a highly statistically significant difference between the study and control group as regard dNK cells density (uNK cells as a percentage of total stromal cells), in control group: low density = 18.5% and high density = 81.5% while in the study group: low density = 96.3% and high density = 3.7%; (Chi square 33.400 FE) and (P. value = 0.000). Conclusion: These findings suggest that low dNK score and density was associated with cases of placental abruption.