A cylinder head of an internal combustion engine having an electrohydraulic valve controller which includes a master unit (12), a slave unit (24), a hydraulic valve (4), a pressure relief space (18) and a pressure space (17) which is arranged in the direction of transmission between the master unit (12) and the slave unit (24) and can be connected to the associated pressure relief space (18) via the hydraulic valve (4). The master unit (12), the slave unit (24), the pressure space (17), the hydraulic valve (4), the pressure relief space (18) and a non-return valve (31) are preassembled in a common hydraulic housing (8), to form a pre-assembled hydraulic unit (3) which is fastened to the cylinder head (1) and which is connected to the hydraulic medium supply of the internal combustion engine via the non-return valve (31). Here, for the initial filling of the pressure relief space (18) and/or of the pressure space (17) with hydraulic medium, at least one filling device (6) is provided which is independent of the hydraulic medium supply, and is formed on the hydraulic housing (8) and has a closure (35).