Because idiopathic sudden deafness is regarded as the result of a cochlear microcirculation disorder, its treatment has been based mainly on vasoactive therapy with little regard for the blood-flow conditions produced by these circumstances. In a group of 16 patients with sudden-onset deafness, we determined blood viscosity at different shear rates, as well as erythrocyte aggregability, deformability, and filterability, and other potentially influential parameters, such as hematobrit, fibrinogen, and leukocyte and platelet count. These values correlated with hearing loss and average recovery after conventional treatment. Our results showed a trend to high blood viscosity in patients in relation to a control group of persons with normal hearing, with a notorious increase in aggregability, which correlated significantly with recovery of hearing capacity, and a decrease in blood filterability, which correlated with average hearing loss. This suggests a potential etiopathogenic mechanism of the disease and an alternative treatment complementary to current treatment.