The authors report observations of surface phonon-polaritons on a long period GaAs/AlxGa1-xAs multiple-quantum-well structure. Both p- and s-polarised measurements have been made with a far-infrared Fourier transform spectrometer fitted with an attenuated-total-reflection (ATR) stage at the output port. The experimental results are compared with theoretical spectra derived by treating the MQW structure as an effective uniaxial dielectric bulk medium. The experimental and theoretical results are in excellent agreement, both qualitatively and quantitatively. Four surface-mode dips and one guided wave dip are observed in p-polarisation at frequencies which are in good agreement with theory and, as expected, no surface-mode features are observed for s-polarisation.