OBJECTIVE To use the meta-analytic approach to examine the effects of aerobic exercise on lumbar spine bone mineral density in postmenopausal women. METHODS Studies were retrieved from computer searches (MEDLINE, Current Contents) as well as cross-referencing from the bibliographies of retrieved studies and review articles. METHODS A total of 17 effect sizes consisting of 330 subjects (192 exercise, 138 nonexercise) were included from the 10 studies that met the criteria for inclusion: (1) aerobic activity as the only exercise intervention, (2) postmenopausal women as subjects, (3) comparative nonexercise group included, (4) changes in lumbar spine bone mineral density reported, (5) studies published in English-language journals between January 1975 and December 1994. METHODS The primary outcome measure of interest was the treatment effect delta3, defined as the percent change in lumbar spine bone mineral density, calculated by subtracting the percent change in the exercise group from the percent change in the nonexercise group. RESULTS Using a fixed effects model, bootstrap analysis (10,000 replications) showed that significant changes in lumbar spine bone mineral density occurred (mean +/- SD = 2.83 +/- 0.77%, 95% confidence interval (CI) = 1.33 to 4.35%). This overall average increase was caused primarily by the loss of lumbar spine bone mineral density in the nonexercise group relative to the exercise group (mean +/- SD, exercise = .32 +/- 2.46%, 95% CI = -0.94 to 1.58; nonexercise = -2.51 +/- 2.69%, 95% CI = -4.60 to -0.96). CONCLUSIONS The results of this meta-analysis suggest that aerobic exercise helps to maintain lumbar spine bone mineral density in postmenopausal women.