A study of the de Haas-Van Alphen effect in caesium by thc pulsed field method, under carefully controlled experimental conditions, has yielded information about the orientation dependence of the Fermi surface cross-section. A computer analysis of the results m terms of cubic harmonic series has mdicated a probable radial distortion of some +3.3% in the  direction, -0.9% in the  direction, and -1.4% in the  direction; this is compared with the predictions of band structure calculations which, though indicating approximately the correct shape of Fermi surface, are appreciably m error as to the magnitude of the deviations from a sphere. The observed Fermi surface distortion is also discussed m terms of its effect on the low temperature thermoelectric power of caesium. The volume of the Fermi surface is found to be within a few tenths of 1% of that calculated from published lattice constant data. Strong variations of signal strength with orientation were observed; these have been attributed in part to the effect of spin-splitting of the Landau levels.