A roof window system comprising at least two window units (11, 12) configured to be built in side by side in a roof structure of a roof, in particular comprising an inclined roof surface, said roof window system furthermore comprising a support assembly configured to be fastened to the roof structure and to which the window units (11, 12) are to be connected, wherein said support assembly comprises a set of support beams (31, 32) configured to be mounted substantially horizontally in said roof structure, and that at least one of a top member (111, 121) and a bottom member (114, 124) of each window unit (11, 12) are intended to be connected with at least one of said set of support beams (31, 32) in a mounted condition of the roof window system, characterised in that the connection between the support assembly and the roof structure is carried out by a set of mounting brackets, that each mounting bracket comprises a base, at least one leg and at least one upstanding flange, that two upstanding flanges are provided and each is connected to the base at a first transition edge of said upstanding flange and each at least one leg is connected to the respective upstanding flange at a second transition edge of said upstanding flange, said first transition edge being preferably perpendicular to said second transition edge, that each leg comprises an inner free side edge portion in extension of the second transition edge of said upstanding flange such that an upper section of each said leg extends above a plane of the base and a lower section of each said leg extends below the plane of the base, that the base, each leg and each upstanding flange comprises at least one hole or aperture adapted to receive fastening means such as screws, and that each leg is provided with a plurality of holes and apertures (426, 427, 428) such that at least one hole or aperture is located in the upper section and at least one hole or aperture in the lower section. wherein said support assembly comprises a set of support beams (31, 32) configured to be mounted substantially horizontally in said roof structure, and that at least one of a top member (111, 121) and a bottom member (114, 124) of each window unit (11, 12) are intended to be connected with at least one of said set of support beams (31, 32) in a mounted condition of the roof window system, characterised in that the connection between the support assembly and the roof structure is carried out by a set of mounting brackets, that each mounting bracket comprises a base, at least one leg and at least one upstanding flange, that two upstanding flanges are provided and each is connected to the base at a first transition edge of said upstanding flange and each at least one leg is connected to the respective upstanding flange at a second transition edge of said upstanding flange, said first transition edge being preferably perpendicular to said second transition edge, that each leg comprises an inner free side edge portion in extension of the second transition edge of said upstanding flange such that an upper section of each said leg extends above a plane of the base and a lower section of each said leg extends below the plane of the base, that the base, each leg and each upstanding flange comprises at least one hole or aperture adapted to receive fastening means such as screws, and that each leg is provided with a plurality of holes and apertures (426, 427, 428) such that at least one hole or aperture is located in the upper section and at least one hole or aperture in the lower section.