A novel grommet assembly for securely sealing a wire harness or cable to an automotive panel opening is achieved with separate, identical grommet halves whose components are axially assembled. The assembled grommet halves are radially mated over the cable and lockingly inserted into the dash panel opening to provide an airtight seal between the cable and the opening. The grommet assembly includes rigid inner and outer shell portions which are axially locked to sandwich a resilient seal therebetween. The seal essentially fills the space between the inner and outer shells, and is both axially and radially compressed upon assembly of the grommet halves, and further when the grommet halves are mated over the cable. The compressive forces on the seal ensure a secure, airtight sealing interface with the cable, between the components of the grommet assembly, and with the dash panel.