The invention relates to a reinforcement beam (3) for a structural part (2) of a motor vehicle body, in particular a side impact protection beam (3) for a side door (2) of the motor vehicle body. A one-piece elongated open metal profile defines a longitudinal axis and has at least one U-shaped main portion (5) with a bottom (6) and two U-legs (7), the bottom (6) forming an outer wall of the metal profile, and at least two flanges (8) extending laterally outwardly form the U-legs (7) of the main portion (5). The main portion (5) and the flanges (8) extend over substantially the entire length of the reinforcement beam (3). The flanges (8) are separated from the main portion (5) over an appropriate length at both longitudinal ends of the main portion (5). The separated end portions (9) of the flanges (8) are adapted to be used for connecting the reinforcement beam (3) to suitable attachment surfaces (10) on the associated structural part (2) of the motor vehicle body.