Attempts have been made to find objective parameters for assessing voice quality for many years. Objective measurements such as the dysphonia severity index (DSI), using four parameters (highest frequency, lowest intensity, maximum phonation time and jitter), appear to correlate well with perceptual evaluation. The aim of this study was to investigate the influence, if any, of age and gender on the DSI. The DSI of 118 non-smoking adults (69 females, 49 males, age range 20-79 years) without voice complaints was measured. Age has a significant effect on the DSI and on its parameters highest frequency and lowest intensity (only in females). Gender has no effect on the DSI, although it has a significant effect on the parameters highest frequency and maximum phonation time. To be able to distinguish between the effects of (normal) ageing and a voice disorder, normative data of a wide age range are essential. As a result of this study normative DSI values for gender and age have been made available.