PURPOSE: As the use of hormone replacement therapy for the menopausal women increases, some caution is advised, since there is an increased risk of breast cancer. Accordingly, the importance of regular mammography has been addressed. This cross-sectional study analyzed the effects of different hormone therapies on mammographic density. MATERIALS AND METHODS: Sixty-seven postemenopausal women who had completed one year of hormone therapy and had undergone follow-up mammography, were divided into two groups : Group I : continuous conjugated equine estrogen, 0.625 mg, plus continuous medroxyprogesterone acetate, 2.5 mg (n=48), Group II : continuous conjugated equine estrogen 0.625 mg (n=19). The mammograms were read by two radiologists. RESULTS: With regard to the radiologists involved, interobserver reliability (kappa) was 0.70 and intraobserver reliability (kappa) was 0.51 and 0.67. Before hormone therapy, factors related to decreased mammographic density were age and number of full term pregnancies (p<0.05). After one year of hormone therapy, body fat showed a significant increase (p<0.05), but in spite of this, increased mammographic density induced by hormone therapy remained significantly high (p<0.05). Compared with Group II, Group I showed a significant increase in mammographic density (p<0.05). In Group I, mammographic density increased from P2 to DY pattern in two cases, but there was no such change in Group II. CONCLUSION: The increase of mammographic density seen in Group II was much more significant statistically than that seen in Group I. The mammograms of women who have undergone continuous combined hormone therapy should therefore be interpreted very cautiously.