OBJECTIVE. The article discusses the fact that for more than 20 years, there has been controversy concerning whether there is a benefit from mammographic screening for women ages 40-49. Based on a decision made many years ago to try to determine how menopause might influence the value of screening, the age of 50 was chosen as a surrogate for menopause. Despite the fact that there are no data to support this age as having any biologic relevance, it continues to be used as if the parameters and benefits of screening change abruptly at the age of 50. CONCLUSION. The data clearly show that the age of 50 is nothing more than an arbitrary age, and it is far from clear whether menopause has any important effect on screening. The "harms" of screening have been cited as reasons for not recommending screening before the age of 50, but since the ratio of harm to benefit changes steadily with increasing age, there is no legitimate rationale for this determination. Women and their physicians should be informed that the age of 50 is an arbitrary threshold in terms of mammography screening so that they can make informed decisions about their own health care.