Collecting contraceptive-use data by means of calendar methods has become standard practice in large-scale population surveys, yet the reliability of these methods for capturing accurate contraceptive histories over time remains largely unknown. Using data from overlapping contraceptive calendars included in a longitudinal study of 3,080 rural Bangladeshi women, we assessed the consistency of reports from the baseline interview month in 2006 with reports from the same month in a follow-up survey three years later, and examined predictors of reliable reporting. More than one-third of women were discordant in their reports for the reference month in the two surveys. Among women reporting use of any contraceptive method for the reference month in both surveys, 25 percent reported different methods at the two time points. Women using condoms or traditional methods and those with more complex reproductive histories, including more births and more episodes of contraceptive use, were least likely to report reliably. (STUDIES IN FAMILY PLANNING