Guidelines have been developed for appropriate posttherapy surveillance for breast cancer recurrence. One purpose of posttherapy surveillance is to detect potentially curable local recurrences and new cancers in the opposite breast. The objective of this investigation was to assess the impact of annual mammography on all-cause mortality in breast cancer survivors. We conducted a case-control analysis nested in a cohort of 865 stage I or II breast cancer patients diagnosed from 1996 to 1999. The exposure variable was the number of mammograms received after completing primary therapy. Cases were decedents and we used risk-set sampling to match eight controls to each case on follow-up time. The mortality rate declined with an increasing number of mammograms (p for trend=0.007). The age- and therapy-adjusted odds ratio associating receipt of an additional mammogram, compared with receipt of no mammogram, equaled 0.77 (95% confidence interval [CI] 0.53-1.1). These results are consistent with a protective effect of regular surveillance mammography after completing therapy for early stage breast cancer.