The clinical records of 889 patients with olfactory disturbance who had been examined at the Olfaction Clinic, Osaka City University Hospital, Japan from January 1982 to December 1996 were studied in order to investigate the relationship between the patients' characteristics and their prognoses. Aetiologically the characteristic variables of "head trauma" and "congenital" had the greatest influence on prognosis, representing poor recovery. The patients with "rhinitis" and "head trauma" showed faster improvement of olfactory disturbance in "females", "those with short duration of olfactory disorder" and "those with high olfactory acuity before treatment". None of the characteristic variables influenced prognosis in the patients with "viral infection". Age did not significantly influence prognosis. Improvement was recognized in most patients within 6 months. Hence, we should treat patients with olfactory disturbance for at least this length of time.