To elucidate the effects of glucocorticoid on bone mineral density in idiopathic thrombocytopenic purpura (ITP) patients, we retrospectively evaluated the relationship between bone mineral density (BMD) and the total dose of glucocorticoid or the mean daily dose given. We found decreased BMD in 66.7% of the patients with ITP to whom glucocorticoid was given, though rather normal bone BMD was observed in 28.6% of ITP patients treated without steroids. The mean level of BMD was markedly decreased in steroid-treated patients compared with steroid non-treated patients (p < 0.01). The relationship between BMD and the total dose of glucocorticoid (p = 0.023) or the mean daily dose revealed a negative correlation (p = 0.022). This study showed that glucocorticoid-induced osteoporosis was observed in patients with ITP, similar to other diseases already reported. When we think of this disease, many cases tend to be followed for a long time, and as the majority of ITP patients is female, we should pay particular attention in the prevention of glucocorticoid-induced osteoporosis.