The aim of the present research was to investigate the influences of cognition on temporal processing of olfactory information in a health-relevant context. We investigated whether expecting an odor to cause adverse health effects alters perception of that odor. An irritation-free odor (Study 1: H(2)S; Study 2: phenyl ethyl alcohol [PEA]) was presented after which participants expected to experience either adverse sensory irritation (caused by intranasal CO(2) presentation) in one condition or no adverse effects in another condition, depending on a previously presented visual cue. Olfactory event-related potentials (OERPs) were measured to assess effects of expectations on the temporal course of olfactory processing. When participants expected irritancy after perceiving the odor of H(2)S, N1 and P3 peak amplitude and N1 latency were increased and shortened, respectively, suggesting more intense and faster processing of the odor as well as effects on salience and anticipation of sensory irritation. When the odor was PEA, only the N1 amplitude was increased. These results, obtained with OERP, provide converging evidence for comparable conclusions regarding the influence of cognition on odor perception reached with functional magnetic resonance imaging. Furthermore, the results suggest that a priori hedonic valence of an odor affects how susceptible the olfactory percept is to modulation via expectations.