The invention relates to a method for determining the set relative position of a patient in a dental panorama X-ray apparatus during which the curvature of a front area of a dental arch of a patient is determined. Set position coordinates for the patient are calculated based on this curvature and on a projection arch surface. In addition, the curvature of a middle area and/or of a rear area of the dental arch is determined and is taken into consideration during the calculation of the position coordinates. During a method for determining the set path of a diagnostic unit, the curvature of a front area of a dental arch of a patient is determined and is fixed at a location in the X-ray apparatus located within the space scanned by an X-ray source and by a detector unit. In addition, the curvature of a middle area and/or of a rear area of the dental arch is determined and a set path curve for the diagnostic unit is calculated based on the measured curvatures. The invention also relates to a device suited for carrying out the aforementioned method.