A voltammetric method based on the adsorption of tin(IV)-catechol complex on a hanging mercury drop electrode is described for the determination of ultra-trace amounts of tin in environmental samples. The interfacial accumulation of the analyte and the use of differential pulse voltammetry during the reduction step provide substantial gains in the sensitivity and permit selective determination of tin in the presence of other elements. Optimal conditions for this method are pH 4.2,1 x 10-4M catechol, and accumulation with stirring at 0.0V versus Ag/AgCl. The detection limit based on the use of the tin peak which occurred at -0.3V versus Ag/AgCl was 5ng/L for an accumulation period of 180s and the relative standard deviation at 50ng/L was 2.2%. The successful application of the method to tin determination in water and sediment samples is reported.