In this paper the effect of the end mill variable pitch on the flatness and surface quality of aluminium (EN AW 6082) thin-walled partswas studied. Tests were performed using the HSC 105 linear CNC machine and following cutting parameters: cutting speeds (800, 100, 1200 and 1400 m.min-1), feed per tooth (0.12 mm), cutting depth (for roughing 10 mm and for finishing 5 mm). Three teethsolid end millsof 12mm diameter with a regular pitch of120° and an irregular pitch of 125°, 130° and 135° were used. Surface analysis of the processed thin-walled parts showed that both the irregular pitch of the end mills and the used cutting speed have a significant influence on the surfacequality of the thin-walled parts. The best results were obtained in the case of 130°, 135°irregular pitch end mills and cutting speed 800 and1000 m.min-1.