Five clinical studies of calcium intake, designed with a primary skeletal end point, were reevaluated to explore associations between calcium intake and body weight. All subjects were women, clustered in three main age groups: 3rd, 5th, and 8th decades. Total sample size was 780. Four of the studies were observational; two were cross-sectional, in which body mass index was regressed against entry level calcium intake; and two were longitudinal, in which change in weight over time was regressed against calcium intake. One study was a double-blind, placebo-controlled, randomized trial of calcium supplementation, in which change in weight during the course of study was evaluated as a function of treatment status. Significant negative associations between calcium intake and weight were found for all three age groups, and the odds ratio for being overweight (body mass index, >26) was 2.25 for young women in the lower half of the calcium intakes of their respective study groups (P: < 0.02). Relative to placebo, the calcium-treated subjects in the controlled trial exhibited a significant weight loss across nearly 4 yr of observation. Estimates of the relationship indicate that a 1000-mg calcium intake difference is associated with an 8-kg difference in mean body weight and that calcium intake explains approximately 3% of the variance in body weight.