X-ray tube construction comprising a housing with a metal tube envelope therein and a shaft. An anode plate is carried by the shaft. Bearings are disposed on opposite sides of the anode plate and rotatably mount the shaft in the envelope. A motor drive is coupled to the shaft for rotating the shaft and the anode plate carried thereby. A cathode is provided for supplying electrons which are accelerated by a high voltage to the anode plate for creating x-rays upon impingement with the anode plate. A heat cage is disposed in the housing and the envelope and surrounds the anode plate. X-ray shielding is disposed within the housing between the envelope and the housing. Windows are provided in the shielding, the metal envelope and in the heat cage to permit x-rays to pass therethrough. Particularly novel means is provided for dissipating the heat generated in the anode and for dissipating the same exterior of the housing prior to the heat passing to the opposite extremities of the shaft. Shaft constructions have been utilized which inhibit the travel of heat to the opposite ends of the shafts and thereby serving to protect the bearings rotatably supporting the shaft.