Dietary intake levels of calcium and magnesium, as well as calcium/magnesium ratios, were assessed for 12 age/sex groups of the U.S. population through use of USDA's 1977-78 Nationwide Food Consumption Survey. Results indicated that a majority of the U.S. population consumed less than recommended amounts (NRC-RDA) of both calcium and magnesium. Approximately 60% of 0 to 5 year olds and 40% of 6 to 11 year olds had average daily calcium intakes of less than 800 mg, while 60 and 85% of the male and female adolescents, respectively, had intakes below the recommended level of 1,200 mg/day. Approximately 80 to 85% of the adult female groups and 50 to 65% of the adult male groups had average intakes below recommended levels. With the exception of children ages 0 to 5 years, the average daily magnesium intakes of all age/sex classes were below the NRC-RDA. Magnesium consumption was particularly low among adolescent females, adult females, and elderly men, with 85, 80-85 and 75%, respectively, of the population groups having average magnesium intakes below their respective NRC-RDA. Furthermore, the majority of the population groups did not consume appropriate proportions of these two minerals to obtain optimal calcium/magnesium ratios. While adolescent females and adult females had more appropriate ratio values than other segments of the population, these ratios principally resulted from their very low intakes of calcium. The most inappropriate calcium/magnesium ratios, observed for children, male adolescents, and young adult males, were, in general, due to their more appropriate calcium intakes and their low magnesium intakes.