The clinicopathologic features of 21 olfactory neuroblastomas are reviewed with emphasis on variables of potential diagnostic or prognostic value. The patients ranged in age from 9 to 66 years (median: 49 years); 57% were women. At the time of diagnosis, one tumor was Kadish stage A, 11 were stage B, and nine were stage C. Nineteen patients had extensive surgical resections, but in six instances these were considered incomplete. Six patients (29%) developed local recurrences and eight (38%) had metastases. Ten patients (48%) were alive and free of disease from 10 to 239 months (median: 58 months) after diagnosis. Seven (33%) died of tumor, with a duration of survival ranging from 1 to 142 months (median: 27 months). A fibrillary intercytoplasmic back-ground was the most useful diagnostic feature microscopically and was present, at least focally, in 18 of 21 tumors. A silver stain for neuronal processes was helpful when fibrils could not be seen on hematoxylin- and eosin-stained sections. Homer-Wright rosettes, when present, also aided in diagnosis but were well formed in only six tumors. The only clinical feature that correlated with prognosis was whether the neoplasm had been completely excised at initial presentation. Tumor necrosis was the only histologic feature correlating with prognosis, but neither association was statistically significant. Metastases, clinical stage, mitotic rate, and nuclear pleomorphism showed no relationship to survival in this series.