Objective: Researchers have identified potential errors in the Gonstead method's analysis of pelvic alignment resulting from y-axis rotation of the pelvis on the anteroposterior (A-P) radiograph. The purpose of this article is to propose a method that can be used to determine the magnitude of y-axis rotation of the pelvis present on the A-P radiograph. Methods: In this proposed method, measurements are obtained from the patient and from the lateral and A-P radiographs. With a mathematical method, these measurements are used with the focal film distance to calculate the degree of pelvic rotation present on an individual A-P radiograph.Results: This method may help with the accuracy of measurement of pelvic y-axis rotation on the A-P radiograph. Conclusion: The method proposed can be used to calculate the magnitude of pelvic y-axis rotation on an A-P radiograph. (J Chiropr Med 2017;16:204-210)