The Small Grain and Grain Crops Institutes, both of the Agricultural Research Council, found that the gross margin of maize monoculture was higher than any other crop rotation system tested in a trial. In this paper the effect of different crop rotation systems on net cash flows are quantified. A whole farm simulation model that incorporates risk was used for this purpose. From a net cash flow point of view maize monoculture was found to be the riskiest. However, the choice of a crop rotation system depends on the risk preference of the decisionmaker since higher risks are also associated with higher profits.