We varied the softness and nodularity of silicone breast models to assess the effects of age-related breast tissue characteristics on lump detection. In two sets of six silicone breast models manufactured to simulate premenopausal and postmenopausal breast tissue, respectively, 82 internal medicine attending and housestaff physicians more readily detected lumps among models simulating older breast tissue. The proportion of models with one or more false-positive findings was higher among models simulating postmenopausal breast tissue. We conclude that age-related changes in breast tissue most likely contribute to the higher sensitivity of clinical breast examination in older women.