Purpose: Vocal hyperfunction, related to abnormal laryngeal muscle activity, is considered the proximal cause of primary muscle tension dysphonia (pMTD). Relative fundamental frequency (RFF) has been proposed as an objective acoustic marker of vocal hyperfunction. This study examined (a) the ability of RFF to track changes in vocal hyperfunction after treatment for pMTD and (b) the influence of dysphonia severity, among other factors, on the feasibility of RFF computation. Method: RFF calculations and dysphonia severity ratings were derived from pre- and posttreatment recordings from 111 women with pMTD and 20 healthy controls. Three vowel-voiceless consonant-vowel stimuli were analyzed. Results: RFF onset slope consistently varied as a function of group (pMTD vs. controls) and time (pretherapy vs. posttherapy). Significant correlations between RFF onset cycle 1 and dysphonia severity were observed. However, in many samples, RFF could not be computed, and adjusted odds ratios revealed that these unanalyzable data were linked to dysphonia severity, phonetic (vowel-voiceless consonant-vowel) context, and group (pMTD vs. control). Conclusions: RFF onset appears to be sensitive to the presence and degree of suspected vocal hyperfunction before and after therapy. The large number of unanalyzable samples (related especially to dysphonia severity in the pMTD group) represents an important limitation.