Abstract: A telescoping adjustment assembly for head positioning means used in a cephalostat. The assembly having sleeves retractably engaged by slide arms, the outward ends of the arms and sleeves carrying brackets for supporting the head positioning means. Substantially no portions of the slide arms or sleeves extend outwardly of the brackets so that the assembly is compact and allows use with tomographic x-ray equipment so that the support portions for the brackets do not shadow the radiograph or provide physical impediments to the rotation of a co-axial x-ray tube and film holder. The assembly is further useful for both fixed-type cephalostats, and angularly adjustable cephalostats of the type wherein lateral and anterior, posterior, and oblique cephalometric studies may be made, wherein the stable, compact adjustment assembly provides very accurate positioning of the cranium, dentition, TMJ, etc.