Can good or bad moods influence people's tendency to rely on irrelevant information when forming impressions (halo effects)? On the basis of recent work on affect and cognition, this experiment predicted and found that positive affect increased and negative affect eliminated the halo effect. After an autobiographical mood induction (recalling happy or sad past events), participants (N = 246) read a philosophical essay, with an image of the writer attached, showing either an older man or a young woman (halo manipulation). Judgements of the essay and the writer revealed clear mood and halo effects, as well as a significant mood by halo interaction. Positive affect increased halo effects consistent with the more assimilative, constructive processing style it recruits. Negative affect promoting more accommodative and systematic processing style eliminated halo effects. The relevance of these findings for impression formation in everyday situations is considered, and their implications for recent affect-cognition theories are discussed. Copyright © 2011 John Wiley & Sons, Ltd.