X-ray tube cooling systems. In one example embodiment, an x-ray tube includes a housing, a window frame attached to the housing, and a window attached to the window frame. The housing defines an aperture through which electrons can pass from a cathode to an anode. The housing also defines an inlet port and an outlet port. The window frame defines an opening through which x-rays can pass. The window covers the opening defined by the window frame. The housing and the window frame are configured such that a liquid can flow from the inlet port to the outlet port through either a first liquid path at least partially defined by the housing or a second liquid path cooperatively defined by the housing and the window frame. The second liquid path is disposed about at least a portion of the opening in the window frame.