A number of studies have demonstrated that radiologists can become fatigued after reading cases for a number of hours. Some of these studies have demonstrated that there are associated decreases in observer performance (i.e., reduced accuracy), but mammographic reading has not been a focus of any of these studies. Based on these recent findings regarding decreases in performance as a function of time of day and/or number of hours reading, this retrospective study examined data from a variety of mammography studies in which readers participated in two sessions - once in the morning and once in the afternoon. The ROC Az data from these studies were compared for statistical differences between morning and afternoon reading. Overall there was a small yet significant (t = 2.365, p = 0.0277) between morning and afternoon diagnostic performance, with performance being degraded in the afternoon. These data suggest that reader fatigue may impact mammography interpretation performance, although more formal studies are required to verify these findings with a prospective study since this retrospective analysis did have limitations.