To evaluate cranial base measurements in different skeletal patterns using Bjork-Jarabak analysis. Objective: To evaluate the linear measurements of the Bjork polygon in different skeletal relationships. To evaluate the angular measurements go the Bjork polygon in different skeletal patterns. Material and Method: 90 pre-treatment lateral cephalograms will be traced using 0.3mm mechanical pencil and lead acetate papers. The age range of the patients was 18-30 years. Patients with a history of previous orthodontic treatment, orthognathic treatment, craniofacial anomalies, facial trauma, or detected asymmetries were excluded. The average mandibular place angle was 27+/- 5 degrees. Cephalometric Analysis: Lateral cephalograms will traced using 0.3mm mechanical pencil on lead acetate sheets. Measurements derived from Bjork-Jarabak analysis included linear and angular measurements. Statistical Analysis: Descriptive statistics (means and standard deviations) will be calculated for all of the measured variables. To assess the differences among groups, analysis of variance was used. Gender differences will be detected using the independent- sample t-test. Statistical significance was predeter- mined as P