The number of life events reported by study participants is sensitive to the method of data collection and time intervals under consideration. Individual characteristics also influence reporting; respondents with poor mental health report more life events. Much current research on life events is cross-sectional. Data from a longitudinal study of women's health from 4 waves over a decade suggest that over time additional systematic biases in reporting life events occur. Inconsistency over time is due to both fall-off of reporting and telescoping. Intracategory variability and ambiguity of items, as well as respondent characteristics, also potentially contribute to response biases. Although some factors (e.g., item wording) are controllable, others (e.g., respondents' mental health) are not and must be factored into data analysis and interpretation. (Contains 3 tables.)