In order to investigate whether nonlinear methods of signal analysis provide a measure of phonatory irregularities in neurogenic voice disorders, the present study computed the fractal dimension(D)both of the electroglottographic (EGG) and the acoustic signal of sustained vowel productions obtained from patients with Parkinson’s disease (PD) and cerebellar atrophy (CA). Compared with normal speakers, the female PD group as well as the male and female CA patients showed an increased dimension(D)of the EGG. The dimensional complexity of the acoustic signal largely depended on vowel type. Furthermore, the dimension of the acoustic signal was reduced in male PD patients as compared to the respective controls.