There is a need for an objective measure that describes normal resonance and resonance disorders. The current standard of practice has not led to mismanagement but a refined objective assessment protocol will benefit a more precise objective assessment of velopharyngeal disorders. The purpose of the present study is to construct a nasality severity index (NSI) that reflects the multidimensional nature of resonance. Objective and subjective assessment techniques were used to determine the nasalance, the nasality and aerodynamic capacities in 21 children with cleft palate and a control group of 25 children without cleft palate. Stepwise logistic regression was used to determine the optimal index. The NSI consists of a linear combination of 4 variables, where each variable has a different weight. The equation is: NSI = -60.69 - (3.24 x percent oral text) - (13.39 x Glatzel value /a/) + [0.244 x maximum duration time (seconds)] - (0.558 x % /a/) + (3.38 x percent oronasal text). NSI sensitivity is 88% and specificity is 95%. Daily clinical use of the NSI has shown it to be an efficient and practical tool to describe the presence of hypernasality. Three distinct follow-up cases are presented to illustrate the impact of a surgical technique, the use of a speech bulb and velopharyngeal biofeedback training on NSI. The implementation of the NSI may help clinicians to quantitatively assess the severity of nasality disorders beside the perceptual judgments.