The hopelessness theory of depression’s (Abramson et al. (1989). Psychological Review, 96, 358–372) cognitive vulnerability-stress hypothesis was tested using data from a 6-week longitudinal study of university undergraduates. Participants completed measures of negative inferential style, negative events, and depressive symptoms at the initial assessment and measures of negative events and depressive symptoms each week for the next 6 weeks. Supporting the vulnerability-stress hypothesis, results of hierarchical linear modeling indicated that inferential styles moderated the relation between weekly negative events and weekly variations in depressive symptom levels. Specifically, participants with negative inferential styles who also experienced high levels of negative events in a given week reported the greatest increases in depressive symptoms during that week. Although we also found that depressive symptoms prospectively predicted changes in negative events from week to week, inferential styles did not moderate this relation.