Numerous dietary supplements are marketed as slimming aids, but the efficacy of most has not been proven. One such slimming aid is calcium. Presented here are the results of a systematic review that aimed to evaluate the evidence for or against the efficacy of calcium supplements for body-weight reduction in overweight and obese individuals. Electronic searches were conducted to identify relevant randomized clinical trials of at least 6 months duration. No restrictions of age, gender, language, or time of publication were imposed. Two reviewers independently determined the eligibility of studies, assessed the reporting quality of the studies included, and extracted data. Twenty-four eligible trials were identified, and seven were included. Five of the randomized clinical trials included were not of good reporting quality. A meta-analysis revealed a small, significant reduction in body weight for calcium compared with placebo (mean difference, (-) 0.74 kg; 95% confidence interval, (-) 1.00-(-) 0.48). A small, significant reduction in body fat favoring calcium over placebo was also noted (mean difference, (-) 0.93 kg; 95% confidence interval, (-) 1.16-(-) 0.71). In conclusion, the evidence from randomized clinical trials suggests calcium supplementation generates small, statistically significant weight loss in overweight and obese individuals, but the clinical relevance of this finding is uncertain.