Nowadays, Cone beam computed tomography is widely used for both diagnosis and treatment planning in many dental fields providing precise three dimensional information about dental and maxillofacial structures with almost infinite number of image display options. Obtaining linear measurements is one of the very helpful facilities provided by all CBCT software and the dentists rely on such measurements for taking the right decision especially as regard implant placement, endodontic treatment as well as in cases requiring orthodontic intervention. The lack of accuracy of these linear measurements may lead to serious problems which might endanger the patient or adversely affect the treatment outcome. The patient’s head position during the CBCT scanning could deviate from the ideal one predetermined by each CBCT machine manufacturers. It is therefore important not only to assess the accuracy of linear measurements obtained from CBCT scans in standard scanning position, but also to examine the effect of improper head positioning on the accuracy of these measurements. Some controversies concerning the influence of changing the head positions on the accuracy of CBCT linear measurements were found on the previous studies. This study aimed to assess the accuracy of linear measurements of Planmeca Promax 3D MID® CBCT machine in both standard and different head positions. Eleven dry human skulls were included in the study. Gutta percha markers were placed to define the distances to be measured in occluso-apical, bucco-lingual and mesio-distal dimensions. These 3 dimensions were measured in anterior, bilateral premolars and bilateral molars regions for each jaw and the skulls were imaged in standard and four different head positions (forward tilt, backward tilt, lateral tilt and rotation). Real measurements were taken using a digital caliper and CBCT measurements were performed by two radiologists separately. Our study results showed excellent inter and intra observer agreement. Additionally, excellent agreement was found between linear measurements obtained from CBCT images in each position and the real measurements taken directly from the skull. The absolute measurement error did not exceed 0.52 mm with a tendency to overestimate the real measurements in all the study regions of all the skull positions. The study results showed that the occluso-apical dimension had the least error compared to the bucco-lingual and the mesio-distal ones. Moreover, no statistically significant difference was found between any linear measurements obtained from CBCT images in any head position.