PURPOSE: The purpose of this study was to describe the mandibular incisor positions for the 24 consonant sounds of the English language. Further aims were to determine if the incisor format for each sound is affected by its position in a word, or by combination with an open or closed vowel. MATERIALS AND METHODS: A total of 30 young adult subjects had their incisal positions determined using an electrognathographic technique during performance of a number of speech tests. RESULTS: The mean values of the 24 consonants, in the vertical direction, showed a range from the intercuspal position of 2.5 mm for a sibilant sound to 11.7 mm for the /H/ sound, and an anteroposterior range of 1.4 mm anterior for a sibilant sound to 1.8 mm posterior for the /M/ sound. The range in the mean lateral dimension was always less than 1 mm on either side of the midline. The placement of a sound in the initial or final position in a word had no effect on the incisal position. The degree of vertical opening was significantly greater for 8 of the consonant sounds when in combination with an open vowel sound. The anteroposterior and lateral positions were unaffected by vowel association. CONCLUSION: The incisor position for consonant sounds is unaffected by initial or final word placement. Some consonant sound positions are affected by combination with an open or closed vowel sound. Sibilant sounds produced a clinically acceptable measure of the most superior and anterior speaking positions in all subjects.