We performed a cluster analysis to classify the audiogram shape in patients with idiopathic sudden sensorineural hearing loss (ISSNHL). We also investigated whether the audiogram shape is a prognostic indicator in the management of ISSNHL. A total of 115 inpatients with ISSNHL treated between 2001 and 2010 were analyzed. The data collected included age, sex, duration of hearing loss at the time of treatment, and the presence or absence of tinnitus, vertigo, diabetes, nystagmus, and canal paresis. A hierarchical cluster analysis was performed using the hearing threshold for each frequency on audiograms as variables. A logistic regression model was used for the prognostic analysis. The audiogram shape was classified into four clusters: (1) crossing horizontally pattern of all tones; (2) up-sloping pattern of low-tone loss; (3) deaf pattern; and (4) down-sloping pattern of high-tone loss. The age of the patient, presence of canal paresis, and audiogram shape showed statistically significant relationships with hearing improvement. The audiogram shape based on the cluster analysis demonstrated a significant relationship with hearing improvement in patients with ISSNHL. Further studies are needed to elucidate the underlying etiology of each audiogram shape.