A roof window system configured for being mounted in an opening in a roof structure of a building, said roof window system including a ventilation unit configured for being mounted adjacent to a roof window and adapted for providing ventilation of the interior of the building in which the roof window is mounted, where said roof window comprises at least one frame defining a frame plane and including a pane mounted in said frame, the frame comprising a top frame member intended for being located highest in the mounted state when seen in the direction of inclination of the roof structure, a bottom frame member opposite the top frame member, and two side frame members (2c, 2d) extending between the top frame member and the bottom frame member, said frame members together form a window structure delimiting a frame opening and each having an interior side intended for facing the interior in the mounted state, an exterior side intended for facing the exterior, an inner side facing the frame opening and an outer side facing away from the frame opening, where the ventilation unit is configured for being arranged primarily adjacent to the outer side of a frame member, and characterized in that the ventilation unit comprises a frame facing side, preferably a lower side, configured for being arranged adjacent to or at the interior side of said frame member and in that the roof window system further comprising a ventilation panel allowing air passage from one side of the ventilation panel to another side of the ventilation panel, thereby defining an intended air flow direction, said ventilation panel being configured for facing the interior of the building and extending away from the interior side of the frame member adjacent to which the ventilation unit is mounted. where said roof window comprises at least one frame defining a frame plane and including a pane mounted in said frame, the frame comprising a top frame member intended for being located highest in the mounted state when seen in the direction of inclination of the roof structure, a bottom frame member opposite the top frame member, and two side frame members (2c, 2d) extending between the top frame member and the bottom frame member, said frame members together form a window structure delimiting a frame opening and each having an interior side intended for facing the interior in the mounted state, an exterior side intended for facing the exterior, an inner side facing the frame opening and an outer side facing away from the frame opening, where the ventilation unit is configured for being arranged primarily adjacent to the outer side of a frame member, and characterized in that the ventilation unit comprises a frame facing side, preferably a lower side, configured for being arranged adjacent to or at the interior side of said frame member and in that the roof window system further comprising a ventilation panel allowing air passage from one side of the ventilation panel to another side of the ventilation panel, thereby defining an intended air flow direction, said ventilation panel being configured for facing the interior of the building and extending away from the interior side of the frame member adjacent to which the ventilation unit is mounted.