PURPOSE: The purpose of our study was to determine the CT and MR imaging features of olfactory neuroblastomas in 15 patients. MATERIALS AND METHODS: Fifteen patients with pathologically proven sinonasal olfactory neuroblastomas were included in this study. MRI was performed in 12 cases, and CT in 11, while eight patients underwent both MRI and CT. Features analyzed included the extent of the tumor at the time of presentation, its size and enhancement pattern, erosion or destruction of bony structures adjacent to the tumor, and intratumoral cystic areas. Metastasis to regional lymph nodes of head and neck area was also evaluated. RESULTS: In all patients, the epicenter of primary tumor was the superior nasal cavity or ethmoid sinuses. In 14 patients, the wall of the nasal cavity including the lamina papyracea was involved, while in 13 there was invo l vement of the cribriform plate. Intracranial tumor extension was demonstrated in nine patients, and intracranial frank mass formation in four. On MR, eight of 12 masses showed low signal intensity on T1-weighted images, while in 11 cases, T2-weighted images revealed iso- or high intensity. In 11 patients, the tumor showed a prominent enhancement pattern on post-contrast enhanced images, while CT scans showed tumor enhancement in all 12 patients. CONCLUSION: Olfactory neuroblastomas generally invade the paranasal sinuses and or-bit,and are at Kadish stage B or C at the time at which symptoms suggest the need for a hospital visit. Intracranial tumor extension of the tumor is frequent, but mass formation large enough to be detected radiologically is seen in less than half of all cases.