The as-cast microstructure, in a cross-sectional slice of a 204-mm diameter vertical direct chill cast billet of AA 6082, was investigated with optical microscopy, backscattered electron microscopy, electron probe microanalysis and Thermo-Calc simulations. The major intermetallic phases present in the billet structure were found to be Al-15(FeMn)(3)Si-2 and Mg2Si. The pi-AlSiMgFe type intermetallic phase was also observed but its presence was limited. Except for the surface region, no obvious difference was found in the distribution of intermetallics across the billet section. For the surface segregation zone (less than or equal to 300 mum in depth), many coarse intermetallic colonies (similar to100 mum) were observed with a volume percentage of about 14.5%, compared with 2% in the centre.