Modal and falsetto registers are the basic vocal qualities used in female speaking voices. The purpose of this study was to identify the frequency at which modal register changed to falsetto register and the frequency range of each modal and falsetto register produced under three loudness levels: soft, comfortable and loud phonations in normal and dysphonic speakers. These data provide information on the relationship between vocal registers. It is hypothesized that vocal pathologies affect the frequency at which register change from one mode to another mode. Fifteen dysphonic and 15 non-dysphonic females were assessed on their ability to produce tone series from the lowest to the highest frequency at soft, comfortable and loud phonations. Fourteen listeners served as judges to identify the first production of falsetto voice in each tone series. The first falsetto tone perceived was considered to represent the frequency at which the modal-falsetto register change occurred perceptually. The change from modal to falsetto register in the tone series occurred between G4 (360.74 Hz) and B4 (485.23 Hz) in the dysphonic group and between A4 (421.00 Hz) and B4 (476.13 Hz) in the non-dysphonic group among the three loudness levels. The results showed that the presence of dysphonia affected the production of vocal registers The dysphonic group demonstrated the modal-falsetto register change at a significantly lower frequency and reduced frequency range in the modal register than those of the non-dysphonic group in the soft and comfortable phonations. In producing falsetto register, the dysphonic group demonstrated reduced ability in producing falsetto register in soft and loud phonations when compared to the non-dysphonic group. Physiological explanations are used to account for the observations.