It is widely assumed in portfolio theory that investors are risk-averse expected-utility maximizers. There is a good theoretical reason for assuming expected-utility maximization. Such behavior is well known to be consistent with several quite plausible postulates of rationality [5]. On the other hand, the main empirical foundation for such behavior in portfolio selection appears to be the observation of diversification. Risk-averse, expected-utility maximization implies diversification in portfolio selection, and investors are observed to diversify.