Background: A healthy olfactory cleft is critical to normal olfactory function. The aim of this study was to explore the differential orthonasal and retronasal olfactory functions in patients with olfactory cleft (OC) obstructions including a combination of OC syndrome, chronic rhinosinusitis with or without nasal polyps (CRSwNP or CRSsNP), and respiratory adenomatoid epithelial hamartoma (REAH). Methods: Patients (n = 93) presenting to an ENT clinic with OC obstruction underwent nasal endoscopy, chemosensory event-related potential (ERP) recordings, and radiologic assessment, and were subsequently diagnosed with OC syndrome, CRSsNP with OC syndrome, CRSwNP in the OC, REAH, and CRSwNP with REAH. Orthonasal and retronasal function were assessed using the complete Sniffin’ Sticks test and a set of 30 powders, respectively. Results: Orthonasal function was lower in patients with REAH and CRSwNP+REAH compared to CRSwNP in OC patients. Retrona-sal function was similarly diminished in REAH compared to CRSwNP in OC. Patients with OC syndrome alone had higher orthona-sal scores than those with CRSsNP plus OC syndrome and CRSwNP in OC but not statistically different retronasal function. There was no significant difference in orthonasal or retronasal scores in REAH patients based on concurrent CRSwNP. Conclusions: REAH corresponded with greater orthonasal and retronasal olfactory loss compared to other olfactory cleft ob-structions, indicating a greater effect on the olfactory mucosa beyond disrupting airflow. The difference between CRS and OC syndrome is more pronounced orthonasally than retronasally.