An inventive ignition coil has a transformer that includes a primary coil, a secondary coil and a core formed from stacked metal sheets. A plastic frame holds the sheets. A housing surrounds an interior in which the transformer is arranged and the interior is sealed with an electrically insulating casting compound. The housing comprises an interior wall bounding bounds a compartment in which a part of the core is arranged, the part of the core being outside the primary coil and the secondary coil.