Keynes in 1937 examined the phenomenon of the Great Depression from a longrun perspective in contradiction to the "General Theory," where the focus was on the shortrun. "Some Economic Consequences of a Declining Population," Keynes' article, reveals the context in which the "General Theory" was written. In the "General Theory," the focus is on short-term fluctuations, i.e., business cycles, but Keynes fails to provide any theoretical explanation as to why the depression of the 1930s was so severe and intractable. In the 1937 article, the depression is seen as the result of the combined effects of a decline in longrun growth due to population growth decline and a shortrun cyclical decline, together producing severe economic consequences. What is important for the purposes of this discussion is the implication, within the context of the 1937 article, that not only was the stock market crash of 1929 related to population change (with its accompanying collapse in expectations) but that, in general, changes in the rate of growth of population are accompanied by stock price movements in the same direction. The remainder of the discussion is devoted to a simple empirical test of this relationship. The data used are population size (POP), defined as the total residential population in the US from 1870-1979, and the Standard and Poor 500 Stock index (SP) for the corresponding 109-year period. In addition, a 3rd series was constructed, a price deflated Standard and Poor index (RSP) with a base period of 1870, to account for possible inflationary distortion of the index. The empirical results do not invalidate the hypothesis that population growth rates affect equity markets. In fact, there seems to be strong evidence that they are related in a manner suggestive of Keynes' intutition, namely, that the stock market crash of 1929 was due to factors more fundamental than those often perceived from a shortrun perspective. According to Keynes (1937), population is the most important determinant of longrun movements in real per capita income (given the state of technology, the real rate of interest, the age structure of the population, and the size share of income). So the focus is on population and its effects on economic growth. Due to the fact that the stock market presumably discounts longrun economic conditions as reflected in equity prices, it would seem that if Keynes were correct in his theoretical speculations, longterm equity price movements should relate to population change. In this sense, the paper may be regarded as an empirical test of a proposition of Keynes. More generally, the paper is suggestive in several ways. The relationship between business cycles and stock market cycles has been understood to the point of being rather obvious, but the effects of population on both has been less clear. It does appear on the basis of the evidence presented that the malaise of the stock market during the past 16 years, especially in real terms, may be due to factors more fundamental than those often perceived.