A case is described in which the orthopantomogram by coincidence showed an anomaly of the left articular eminence of the temporal bone, which is based on an extremely pneumatised mastoid bone. Because of the medical history a CT-scan was made of both temporomandibular joints. The CT-scan showed an extremely pneumatized articular eminence at the left side. The orthopantomogram might show a radiolucency in the articular eminence of the temporal bone as a coincidental appearance. In cases with a positive medical history for pathological deformaties or in cases where surgery has to be performed on the articular eminence of the temporal bone further radiodiagnostic examination is indicated.