A variety of non-photorealistic rendering styles include lines extracted from 3D models. Conventional visibility algorithms make a binary decision for each line fragment, usually by a depth test against the polygons of the model. This binary visibility test produces aliasing where lines are partially obscured by polygons or other lines. Such aliasing artifacts are particularly objectionable in animations and where lines are drawn with texture and other styl-ization effects. We introduce a method for anti-aliasing the line visibility test by supersampling, analogous to anti-aliasing for polygon rendering. Our visibility test is inexpensive using current graphics hardware and produces partial visibility that largely ameliorates objectionable aliasing artifacts. In addition, we introduce a method analogous to depth peeling that further addresses artifacts where lines obscure other lines.