This is a randomized, double-blind, placebo-controlled trial of 24 months in which juvenile rheumatoid arthritis (JRA) patients will take either an oral calcium supplement of 1,000 mg elemental calcium per day or a matching placebo containing no calcium (Ca), plus one multivitamin per day. We hypothesize that patients receiving calcium supplementation will demonstrate at least a 10 percent greater increase in total body bone mineral density compared to those treated with placebo.