For small batches, prototypes and customized mass production, additive manufacturing is a prominent technology for the production of complex thermoplastic parts. A frequently used process is the Fused Deposition Modeling (FDM). For more and more applications additive manufactured components have to be combined with conventionally produced structures in order to form larger functional assemblies. Laser transmission welding (LTW) of thermoplastics is an industrial established technique, e. g. for joining injection molded parts in the automotive sector. These parts are typically homogeneous in their structure. However, the FDM process itself results in an inhomogeneous structure because the part is build up layer by layer. The printer nozzle moves in the horizontal plane to generate a layer on the build plate by deposition of thermoplastic strands. For the next layer the build plate moves vertically and the deposition starts again. There are different types of filling strategies to build a layer. First an outer wall is formed and then the infill is performed by rasterizing or concentric motion of the printer nozzle. In order to use LTW for the joining of additive manufactured components there is a large need to obtain basic knowledge of the inhomogeneous structure of generated parts with regard to the optical behavior. Therefore, this paper presents fundamental studies of the influence of main FDM parameters, such as layer height, infill strategy, distance between the strands and the component thickness on LTW. For the investigations specimens of transparent polylactide (PLA) were manufactured as the transparent welding part and specimens of black PLA as the absorbing welding part. To find relationships between the FDM parameters and the optical transparency, the light propagation through the transparent specimen was measured by optical spectroscopy at the wavelength of 940 nm, which is the wavelength of the used diode laser for the LTW experiments. The PLA specimens were welded in overlap configuration with different energy per unit length. Shear tensile tests were performed with the welded samples and cross sections were prepared to examine the influence of the FDM parameters on the weld seam characteristics. A significant influence of FDM parameters on the optical transparency and therefore on the LTW process has been determined. Based on the results guidelines for the FDM process are derived to increase the weld seam strength.