The efficacy of combined high-dose steroid and PGE1 treatment initiated immediately after the onset of sudden deafness was analyzed with the outcome of 174 patients begun on treatment within 7 days of the onset of sudden deafness. Four potential prognostic factors (days from onset to treatment, age, initial hearing level, presence of vertigo) and hearing outcome were examined with a multiple logistic regression analysis. Days from onset to treatment and age significantly correlated with hearing improvement. The efficacy of the treatment of patients begun on treatment within 3 days of the onset was significantly better than that of patients on treatment 4-7 days after the onset (p < 0.001). In the examination of patients younger than 50 years, the efficacy of the treatment of patients begun on treatment within 3 days of the onset didn't differ significantly from that of patients on treatment 4-7 days after the onset. On the other hand, in the examination of patients aged 50 years and older, the efficacy of the treatment of patients begun on treatment within 3 days of the onset was significantly better than that of patients on treatment 4-7 days after the onset (p < 0.001). These results suggest that significant efficacy may be expected from the combined high-dose steroid + PGE1 treatment, if its use is started within 7 days of the onset of sudden deafness, and started within 3 days of the onset of sudden deafness in patients 50 years old and older.