The aim of this study was to investigate the differences in the in vivo degradation behaviour of magnesium implants with various grain sizes and damaged surfaces. For this purpose, three different LAE442 magnesium implants were produced: cast, single and double extruded implants, in order to obtain different grain sizes. Furthermore, defects were positioned on the surfaces of some of the single extruded implants. The initial stability was determined. Four pins of each implant material were implanted into rabbits' tibiae and regularly clinically, radiologically and μ-computed tomographically investigated over a period of 27 weeks. Following explantation, investigations were carried out using stereo and scanning electron microscopy including energy-dispersive X-ray analyses. Weight and strength changes were measured. The double extruded implants possessing the finest grains exhibited the highest initial stability (179.18 N). These implants demonstrated the lowest in vivo corrosion rates (0.0134 mm/year) and the least radiologically visible changes. The highest corrosion rate was computed for the implants possessing damaged surfaces. Radiologically discernible bone changes occurred at almost the same time as implant changes for all groups. Based on these results, the aim should be to produce fine-grained magnesium-based alloys for resorbable implants and to avoid any surface damage. © IMechE 2013.