A quantitative and regiospecific method for attaching azide groups onto the aromatic rings of polysulfone and poly(aryl sulfone) is reported. Polysulfones were activated either on the ortho-sulfone sites or the ortho-ether sites by direct lithiation or bromination-lithiation. The Lithiated intermediates were converted quantitatively to azides by treatment with tosyl azide. Polysulfones containing one, two, and three azide groups per repeat unit were obtained, the degree of substitution being determined by the degree of lithiation. The structures were confirmed principally by NMR spectroscopy. TGA and GPC data are also reported. Soluble aryl azide modified polysulfones were readily isolated and are especially useful for facile conversion to primary amines. This conversion as well as the 1,3-dipolar cycloadditions of these azides will be reported separately.