In all of 100 consecutive patients referred for retinal angiography with a clinical diagnosis of probable or possible papilloedema a definite diagnosis was made from neurological assessment, neuroradiological investigations, and follow-up. The cases have been divided into 2 groups--those with proved papilloedema and those which have been called either normal or pseudopapilloedema. In all cases the retinal angiograms showed normal or increased optic disc vascularity and normal or increased early and late disc fluorescence. On the basis of these alone clear differences could be shown between the groups. All cases with papilloedema showed a combination of either excess late fluorescence with excess early fluorescence or excess late fluorescence with excess disc vascularity. Only 2 cases of pseudopapilloedema (both with optic disc drusen) showed this combination, and in both the pattern of disc fluorescence was different from that seen in papilloedema. Retinal angiography therefore seems to be of considerable value in differentiating true from pseudopapilloedema, though this is possible only when each stage of the angiogram is carefully studied.