Abstract: A cylinder head of an internal combustion engine is disclosed with an upwardly open spark plug tube (1), a connection thread (6) present on the end of the spark plug tube for screwing the spark plug into the cylinder head (3) and with a sleeve (2), which is inserted into the spark plug tube and accommodates the spark plug. The spark plug tube is provided with an increased diameter (D) cut through at right angles to a longitudinal direction thereof. A process for manufacturing such a cylinder head is described, in which the internal diameter (d) of the spark plug tube (1) is first increased to a diameter (D) that is larger than the external diameter of the sleeve (2) by a material-removing process, the spark plug tube (1) is subsequently cut through at right angles to its longitudinal direction, and the sleeve (2), wetted with the permanently elastic sealant, is finally inserted into the spark plug tube (1) and is adjusted therein.