OBJECTIVES: This pilot study compared a prototype electronic menstrual calendaron a handheld computer with a paper calendar for data quality and participants'perceptions.DESIGN: Twenty-three women completed identical information about menstrualbleeding and symptoms using paper and electronic calendars for 1 month each.RESULTS: Use of the paper calendar resulted in more missing data than theelectronic calendar for bleeding characteristics (13% vs. 4%) and symptoms (35%vs. 4%). The electronic calendar's ability to log data entries revealedretrospective entry for 61% of the data. Total data entry and cleaning time wasreduced by 81% with the electronic calendar. Overall, participants preferred the electronic (70%) to the paper (22%) calendar.CONCLUSIONS: Data quality with conventional paper calendars may be poorer thanrecognized. The data-logging feature, unique to the electronic calendar, iscritical for assessing data quality. Electronic menstrual calendars can be usefuldata collection tools for research in women's health.