The invention relates to an environmentally sealed plug-in connector housing formed from a base body (2) having a fastening flange (10) molded thereon. The fastening flange (10) is associated with a sealing element (20) that is compressed in a sealing manner between the fastening flange (10) and an assembly surface (3). In order to ensure the sealing of fastening bores (11) provided in the fastening flange (10), sealing sleeves (21) are molded onto the sealing element (20), which sealing sleeves extend into the fastening bores (11) and at least completely pass through the latter. A fastening screw inserted into a fastening bore (11) can in this way seal with its screw head the fastening bore (11) by means of the sealing sleeve (21) that is compressed by the screw head.