Undoped and Mn2+-doped CdSe nanowires (NWs) grown by a solution–liquid–solid (SLS) method using Bi nanocatalysts have been studied by X-ray powder diffraction measurements. Except for heavily doped nanowires no measurable changes in nanowire lattice parameters were observed. The lattice parameter of heavily doped nanowires shrinks by about 0.5% compared with the undoped ones, which corresponds to a doping concentration of 1.6%. For the other samples no change in lattice parameter is measured referring to a doping level much below 1%. Real structural parameters of nanowires were found to vary as a function of doping level, such as the zinc blende to wurtzite ratio, the static Debye–Waller factor, axial strain, and the number of stacking faults. Compared with the undoped nanowires the overall perfection is slightly improved for low doping but deteriorates drastically for higher doping. Our results highlight the importance of controlling the dopant concentration during the preparation of doped nanostructures.