System of a reinforced structural element (12, 14) of a motor vehicle, the system comprising: a structural element (12, 14) which comprises a first panel sheet and a second panel sheet, wherein the panel sheets (4, 5) are interconnected at a first joint and at a second joint, and wherein the panel sheets (4, 5) form an elongate cavity in the region between the first joint and the second joint, and wherein the panel sheets (4, 5) form a first region (4.1, 5.1), a second region (4.2, 5.2) and a third region (4.3, 5.3) in each case between the joints (6, 7); a reinforcing element which comprises a first side wall, a second side wall, and a connecting wall connecting the side walls (21, 22), and which is disposed in the cavity of the structural element (12, 14); and adhesive which adhesively bonds the reinforcing element to the structural element; characterized in that the reinforcing element is adhesively bonded to a first pair of mutually opposite regions (4.1, 4.2, 4.3, 5.1, 5.2, 5.3) of the panel sheets (4, 5), and to a second pair of mutually opposite regions (4.1, 4.2, 4.3, 5.1, 5.2, 5.3) of the panel sheets (4, 5), and in that the connecting wall comprises a first part-wall (23.1) and a second part-wall (23.2), wherein the first part-wall (23.1) and the second part-wall (23.2) interconnect in each case the first side wall and the second side wall, wherein the first side wall in the region of the first joint is adhesively bonded to the first panel sheet and to the second panel sheet by way of the continuous layer of adhesive, and wherein the second side wall in the region of the second joint is adhesively bonded to the first panel sheet and to the second panel sheet by way of a continuous layer of adhesive. a structural element (12, 14) which comprises a first panel sheet and a second panel sheet, wherein the panel sheets (4, 5) are interconnected at a first joint and at a second joint, and wherein the panel sheets (4, 5) form an elongate cavity in the region between the first joint and the second joint, and wherein the panel sheets (4, 5) form a first region (4.1, 5.1), a second region (4.2, 5.2) and a third region (4.3, 5.3) in each case between the joints (6, 7); a reinforcing element which comprises a first side wall, a second side wall, and a connecting wall connecting the side walls (21, 22), and which is disposed in the cavity of the structural element (12, 14); and adhesive which adhesively bonds the reinforcing element to the structural element; characterized in that the reinforcing element is adhesively bonded to a first pair of mutually opposite regions (4.1, 4.2, 4.3, 5.1, 5.2, 5.3) of the panel sheets (4, 5), and to a second pair of mutually opposite regions (4.1, 4.2, 4.3, 5.1, 5.2, 5.3) of the panel sheets (4, 5), and in that the connecting wall comprises a first part-wall (23.1) and a second part-wall (23.2), wherein the first part-wall (23.1) and the second part-wall (23.2) interconnect in each case the first side wall and the second side wall, wherein the first side wall in the region of the first joint is adhesively bonded to the first panel sheet and to the second panel sheet by way of the continuous layer of adhesive, and wherein the second side wall in the region of the second joint is adhesively bonded to the first panel sheet and to the second panel sheet by way of a continuous layer of adhesive.