The utilization of the laser welding process with filler wire addition is often considered a complicated and difficult process which has too high accuracy demands for a work shop floor. This study shows the effect of some of the most important welding variables to the quality and efficiency of laser welding when welding with filler wire. The material used was a common structural steel St52/37 of 6 mm in thickness. The joint type used was a butt joint. Acceptable weld quality was achieved with most of the tested parameter combinations. The effect of the wire feeding parameters for the acceptable weld quality was smaller than expected. The variations of weld quality caused by the nonoptimized aiming of filler wire can be compensated by the adjustment of the filler wire feed rate and the heat input. The quality of the welds was compared with developed weld quality index. The increase in heat input will make it possible to accept wire feeding to a lower position or from backwards compared to the welding direction. The misalignment of wire in the transverse direction to welding direction and laser beam optical axis causes problems that may lower the quality of the weld. The comparison of the welds with variable air gap widths showed that the weld width is more dependent on the heat input that on the original gap volume.