Introduction: Clinical measurements in the frontal view underevaluate chin deviation in mandibular asymmetry. The aim of this descriptive study is to search for a reliable method of measuring deviant chins using a facial X-ray as reference. Material and method: Seventy patients with mandibular asymmetry who had consulted a maxillofacial surgeon were systematically included. Age, sex, cephalometric characteristics, reasons for patient consultation and type of surgery were collected. Two cephalometric methods were tested with respect to the medial sagittal plane (PSM) to compare the assessment of mandibular asymmetry on soft tissue and by cephalometry. Results: On average, the patients selected were young (26 years +/− 9), women (75% of cases), presented open bite (average FMA: 28° +/− 8°), a skeletal class III tendency, a left-side shift of the chin (63% of cases). They consulted for both aesthetic and functional reasons (51% of cases) and required bimaxillary surgery (66% of cases). Comparison between the photographic angle (formed by the PSM and the line passing through the nasion and reaching the chin point) and the radiographic angle (formed by the PSM and the line passing through the Crista Galli process and the bony chin point angle) showed no significant difference (p = 0.937) and is thus reliable.