Water balance models have been used to examine trends in the level of Lake Victoria over this century. A monthly model developed in a previous study for the period 1925 to 1978 has been improved and the simulation period extended to 1990. Also, an annual model has been used to extend the water balance back to the start of the century. The simulations confirm the results from previous studies which showed that the observed variations in lake level can be explained primarily in terms of natural variations in rainfall over the lake and surrounding basin. An idealized interpretation of these variations is presented which illustrates the long response time of this large lake and which is used to speculate on the likely future behaviour of the lake.