Despite recent controversies in mammography efficacy, encouraging women to obtain regular screenings is still an important public health priority. Published articles about repeat or regular screening were reviewed to determine trends in rates of mammography adherence. A search of MEDLINE and PsycINFO from January 1990 to December 2001 identified 45 empirical articles of U.S. samples that reported, or provided sufficient data to calculate, the percentage of women 50 years of age and older who obtained 2 or more consecutive, on-schedule mammograms. Keywords used in the searches included pairing mammography with regular, repeat, adherence, compliance, annual, rescreen, and maintenance. The weighted average repeat mammography percentage across all eventually included studies (N = 37) was 46.1% (confidence interval: 39.4%, 52.8%). There was no substantial difference in the average repeat screening percentages comparing studies that collected data from 1995 to 2001 versus 1991 to 1994. Within each of 3 time periods of data collection (pre-1991, 1991-1994, 1995-2001), there was substantial variation in repeat rates. This variation appears to be due to several characteristics of study design and sampling, including the definition/methods of collecting data about the adherence measure, prior mammography status, and use of an upper age limit at recruitment. Consensus is needed regarding the definition of repeat mammography. National surveys must include items to assess repeat mammography in order to have estimates that accurately represent population-level rates. Although this study involved mammography, similar challenges in assessing prevalence rates can occur with other screening behaviors.