An empirical isotherm is presented for the physisorption of multilayers in the pressure range from the saturated vapor pressure to the pressure corresponding to monolayer coverage. The isotherm equation is theta = V/V-m ((2n - 1)psi)/(1 - psi))(1/n), where V is the amount adsorbed and V-m is the amount adsorbed in a monolayer, psi = p/p(s) (p is the pressure and p(s) is the saturated vapor pressure), and n lies between 2.5 and 4.5 in most cases. It is shown than this empirical isotherm approaches the Frenkel-Halsey-Hill or MacMillan-Teller isotherms for psi > 0.7 and approaches the Brunauer-Emmett-Teller (BET) isotherm for psi < 0.3. The empirical isotherm is compared with published experimental data for the adsorption of N-2, Ar, H2O, and neopentane on several nonporous solids; the agreement is good from theta = 1 to 3 in most cases and in some cases to theta = 10. A method is outlined for deriving monolayer coverage from a plot of log V against log psi/(1 - psi). For several sets of experimental data for the adsorption of the above gases on nonporous surfaces the monolayer coverage so determined is in agreement with that measured by the BET method to better than 10%.