Carotid body tumors (CBTs), known as neuroendocrine tumors, are generally localized near carotid bifurcation that primarily originating from paraganglionic corpuscles. CBTs are rare tumors with an incidence ranging between 0.06-3.3:100000 (1). Although they are commonly benign and grow slowly, they may cause symptoms such as local pulse-like vibratory sense on the mass site, headache, vertigo or alterations in voice as result of compression effect or cranial nerve dysfunction (2-4). The exact etiological factors of CBTs are unknown. Carotid body is a chemoreceptor detecting the oxygen tension of systemic arterial blood. These tumors were associated with the conditions of chronic hypoxia such as high altitude (5,6). The first information about relationship between gastric cancer and blood group A was mentioned by Aird et al. (7). Many studies were performed for detecting association between blood group of ABO and mechanism of different cancers but its role in CBTs is unknown (8,9). Therefore, the purpose of our study was to review the gender, tumor diameters and ABO blood group of patients with CBTs by comparing these findings with healthy controls. Material and Methods The demographic and laboratory data of 65 CBTs patients (57 females and 8 males) who underwent surgical intervention from January 2007 to June 2017 and 65 age-matched healthy controls were obtained from information system of the hospital. Age, gender, complete blood count parameters and AB0 blood groups of all study participants were evaluated. The tumor diameters were also measured in the patient group. Patients with the missing records were not included in this study.