X-ray tube and method for determination of focal spot properties The invention relates to an x-ray tube (1) comprising at least one cathode (3) which emits electrons accelerated towards a rotating anode (5) such that the focal spot (27) is formed on a surface (9) of the anode (5). A structure (15), in particular slits or pits (13), is disposed on the surface (9) of the anode (5). The x-ray tube (1) comprises a detector (7) for detecting a detection signal which changes, if the structure (15) on the rotating anode (5) passes the focal spot. The x-ray tube (1) further comprises determination means (6) for determining properties of the focal spot from changes of the detection signal. Thus, properties of the focal spot can be determined from changes of the detection signal during operation of the x-ray tube (1).