A side airbag system is provided with a side airbag for protecting the upper thorax and head area of a vehicle passenger between a lateral vehicle structure and the vehicle passenger, and with a gas generator that is fluidically connected with the side airbag. The side airbag is planar in the deployed condition, and protectively covers a path of motion for the head, along with various seated positions for small and large vehicle passengers. In order to realize an expanded protective potential for the head in semi-convertibles and compact cars, the side airbag, viewed from the lateral vehicle structure, has an outer contour with an essentially continuous bead.