Conclusions: The olfactory and intranasal trigeminal systems are closely connected. With regard to intranasal trigeminal event-related potential (ERP), patients with olfactory dysfunction (OD) showed longer latency and lower amplitude, which indicated decreased trigeminal sensitivity. Different age, etiology, and olfactory status also affect trigeminal sensitivity differently. Objective: OD is a common symptom in the rhinology clinic. ERP is considered an important method to evaluate chemosensitivity. The aim of this study was to investigate changes of intranasal trigeminal sense in patients with postviral OD (PVOD) and post-traumatic OD (PTOD). Methods: A total of 96 participants (30 healthy adults and 66 patients with OD) aged 20-65 years were investigated. The T&T olfactometer, the Sniffin' Sticks olfactory test, and trigeminal ERPs (tERPs) were used. We evaluated trigeminal sensitivity influenced by different factors (age, etiology, and olfactory status) in healthy subjects with normal olfactory function and in patients with PVOD and PTOD. Results: Patients with OD showed higher trigeminal thresholds than normal controls. Compared with controls, N1/P2 latencies of tERPs increased and amplitudes decreased in patients with OD. Older subjects showed longer latencies and lower amplitudes than young subjects in both controls and the OD group. Patients with PTOD exhibited worse psychophysical olfactory function and decreased trigeminal sensitivity.