Background: Pronounced chemosensory adaptation affects many patients with olfactory loss. The study aimed to investigate adaptation to olfactory and trigeminal nasal stimuli in patients with olfactory loss in comparison to controls using electrophysiological measures. Methodology: Thirty-four patients with olfactory loss (mean age ± SD = 59 ± 16 years) and 17 healthy volunteers (mean age ± SD = 50 ± 14 years) were recruited. Sniffin’ sticks test was used for evaluation of olfactory function and EEG-derived chemosensory event-related potentials were recorded. Intranasal stimuli were presented using high-precision, computer-controlled stimulators based on the principles of air-dilution olfactometry. Data were analyzed in two different approaches according to the relatively short or long inter-stimulus interval. A decreased peak amplitude or a prolonged latency was considered as an expression of adaptation. Results: The majority of participants (88%) responded reliably to chemosensory stimulation. Patients with olfactory loss exhibited pronounced olfactory and trigeminal adaptation within the long-term design, without such effects in healthy controls. Odor sensitivity correlated with both olfactory and trigeminal amplitude changes: the worse the olfactory sensitivity, the more pronounced chemosensory adaptation. Conclusions: The results help to explain the patients’ complaints in terms of the fast adaptation towards chemosensory stimuli, for example during eating and drinking. The differences in adaptation in patients with olfactory loss and healthy controls could serve as a clinical criterion to gauge olfactory dysfunction.