Objectives: This pilot study compared a prototype electronic menstrual calendar on a handheld computer with a paper calendar for data quality and participants' perceptions. Design: Twenty‐three women completed identical information about menstrual bleeding and symptoms using paper and electronic calendars for 1 month each. Results: Use of the paper calendar resulted in more missing data than the electronic calendar for bleeding characteristics (13% vs. 4%) and symptoms (35% vs. 4%). The electronic calendar's ability to log data entries revealed retrospective entry for 61% of the data. Total data entry and cleaning time was reduced 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 than recognized. The data‐logging feature, unique to the electronic calendar, is critical for assessing data quality. Electronic menstrual calendars can be useful data collection tools for research in women's health. (Menopause 2000;7:200‐208. © 2000, The North American Menopause Society.)