BACKGROUND CONTEXT The role of the cranio-cervical complex in spinal sagittal alignment has rarely been analyzed and described but it may play a fundamental role in postoperative mechanical complications. PURPOSE The aim of the study is to analyze the normative value of the cervical inclination angle for each thoracic vertebra in an adult asymptomatic multiethnic population. STUDY DESIGN/SETTING Observational study; multiethnic cohort study. PATIENT SAMPLE Multiethnic cohort of adult asymptomatic volunteers. OUTCOME MEASURES Measurement of the cervical inclination angle of each thoracic vertebra in adult asymptomatic volunteers using stereoradiography according to patient's age and ethnicity. METHODS Standing full-spine EOS imaging of adult asymptomatic volunteer subjects from five different countries (France, Japan, Singapore, Tunisia and USA) were analyzed. The cervical inclination angle was first analyzed globally and then in each decade of life (<20 years; 21-30 years; 31-40 years; 41-50 years; 51-60 years; 61-70 years; 71-80 years). Different ethnicities were compared. Comparisons between different age and ethnicities groups were performed using a t-test and statistical significance was considered with a p value <0.05. RESULTS EOS images of 468 volunteers were analyzed. The global mean cervical inclination angle was 80,2° with a maximum difference of 9° between T1 and T12 (p <0,001; range 77,05° to 86,05°). The CIA angle remains constant until 60 years old then it decreases significantly passing from a mean value before 20 years old of 82,25° to 73,65° after 70 years old. A statistically significant difference was found between the Arabic and all other ethnicities with the former having an inferior CIA angle: this was related to a mean older age (45,48 vs 39,35 years; p < 0,05) and higher BMI (27,13 vs 23,86 Kg/m2; p <0,05) in the Arabic population. CONCLUSIONS The cervical inclination angle remains constant through age until 60 years-old and reduces slightly but never lower under 70°. This angle might be a helpful tool to evaluate the lever arm on the thoracic spine after an ASD surgery and could predict the occurrence of a proximal junctional kyphosis when its value is lower than normal. Further clinical studies must confirm this theory, particularly in surgically treated patients with long fusion. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. The role of the cranio-cervical complex in spinal sagittal alignment has rarely been analyzed and described but it may play a fundamental role in postoperative mechanical complications. The aim of the study is to analyze the normative value of the cervical inclination angle for each thoracic vertebra in an adult asymptomatic multiethnic population. Observational study; multiethnic cohort study. Multiethnic cohort of adult asymptomatic volunteers. Measurement of the cervical inclination angle of each thoracic vertebra in adult asymptomatic volunteers using stereoradiography according to patient's age and ethnicity. Standing full-spine EOS imaging of adult asymptomatic volunteer subjects from five different countries (France, Japan, Singapore, Tunisia and USA) were analyzed. The cervical inclination angle was first analyzed globally and then in each decade of life (<20 years; 21-30 years; 31-40 years; 41-50 years; 51-60 years; 61-70 years; 71-80 years). Different ethnicities were compared. Comparisons between different age and ethnicities groups were performed using a t-test and statistical significance was considered with a p value <0.05. EOS images of 468 volunteers were analyzed. The global mean cervical inclination angle was 80,2° with a maximum difference of 9° between T1 and T12 (p <0,001; range 77,05° to 86,05°). The CIA angle remains constant until 60 years old then it decreases significantly passing from a mean value before 20 years old of 82,25° to 73,65° after 70 years old. A statistically significant difference was found between the Arabic and all other ethnicities with the former having an inferior CIA angle: this was related to a mean older age (45,48 vs 39,35 years; p < 0,05) and higher BMI (27,13 vs 23,86 Kg/m2; p <0,05) in the Arabic population. The cervical inclination angle remains constant through age until 60 years-old and reduces slightly but never lower under 70°. This angle might be a helpful tool to evaluate the lever arm on the thoracic spine after an ASD surgery and could predict the occurrence of a proximal junctional kyphosis when its value is lower than normal. Further clinical studies must confirm this theory, particularly in surgically treated patients with long fusion.