The degree to which under nourishment exists in a local community such as San Diego, California, and in the U.S. at large, and whether it is severe enough to interfere with brain development is the focus of this report. After establishing criteria for nutrition intake that would represent unambiguous jeopardy to brain development, these criteria are applied to the two best available sources of nutritional and developmental evidence based on large and presumably representative populations in the U.S. Results indicate that, as of 1970, more than two million pregnant women, infants, and children under four years of age are under nourished to such a severe degree that the brain development of the unborn and young child is in jeopardy. Evidence is also found that indicates that nutritional intake, blood and urinary bio-chemistry, and anthropometric measures are deficient but tend to be ameliorated as family incomes rise. The presumptive outcome of such severe under nutrition may be the introduction into the U.S. school systems and ultimately into adult society between one-third and one-half million youngsters annually who may be lastingly or permanently handicapped in relation to functions that depend upon brain structure and organization. The criteria used for predicting jeopardy to brain development deliberately selected to be conservative should be reconsidered. (Author/AM)