Aberrant crypt foci (ACF) are putative precursors of colorectal adenomas and have been postulated as a potential biomarker for colorectal cancer. Few studies have followed subjects after ACF removal to monitor recurrence. Subjects enrolled in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial were recruited for a study of ACF. A standardized protocol using magnified endoscopy and mucosal staining with methylene blue was implemented to detect rectal ACF. After removal of all baseline ACF, subjects returned 1 year later and recurrent ACF were observed and biopsied. A total of 434 of 505 (86%) subjects observed at baseline returned for the year 1 exam. The mean number of ACF at year 1 was strongly correlated with the number at baseline; subjects with 0, 1, 2 to 3, 4 to 6, and 7+ ACF at baseline had a mean of 1.2, 1.4, 1.7, 3.0, and 5.5 ACF, respectively, at year 1. ACF prevalence and mean count at year 1 (61% and 1.93, respectively), were only slightly lower than the corresponding values at year 0 (69% and 2.25, respectively). The locations of ACF at year 1 and baseline were significantly correlated. Of 96 ACF assessed for histology, 70 (73%) were hyperplastic and none were dysplastic. After removal of ACF at baseline, ACF counts 1 year later were only slightly reduced and were significantly correlated with the baseline ACF count. The results of this study do not support a role for ACF in clinical practice.