The presence of surface defects, such as streaking, is one of the most serious quality issues for 6000-series aluminium extrusions. The formation of a streaking defect near a web intersection of a hollow profile was investigated in detail. The streak was apparent on the extrusion in both the as-extruded and the as-anodised conditions. Microstructural examinations indicate that the streaked region contains different surface imperfections compared to the normal region and smaller grains and stronger texture than the normal region. The effects of die design and microstructural variables on the formation of streaks on aluminium extrusions are discussed.