Results of strains from finite element calculations and measurements by the neutron diffraction method in a hollow welded steel beam profile are presented. To calculate the residual strains, each step in the manufacturing process has to be simulated. The D-shaped beam profile is built up by a plate which is flanged into a U-cross-section profile and then welded together with a plate on the top edges. The finite element analysis includes simulation of the manufacturing of the cross-section by bending where large deformations are accounted for. Then, the finite element simulation of the welding pass follows. Plane strain conditions were assumed. The material was assumed to be thermoelastic--plastic, with temperature dependent mechanical material properties. To verify the calculations, measurements of strain were made at approx 40 points, in three orthogonal directions, using the neutron diffraction method. The neutron technique differs from the established X-ray diffraction in the way that the neutrons can penetrate substantial distances into the interior of components which the X-ray cannot. Graphs. 9 ref.-