Apparatus for elevating, laterally and rotationally positioning an aerial work platform relative to a support structure such as a mobile vehicle. In one embodiment a platform supporting carriage is mounted for sliding movement along a support beam affixed to a boom and the platform is mounted on the carriage permitting rotation of the platform about a substantially vertical axis. In a second embodiment a four bar linkage is used for longitudinally moving a rotatable platform. One or more powered means may be provided for elevating, leveling and longitudinally and rotationally positioning the work platform.