Purpose: The purpose of this study was to prospectively examine changes in gender-related voice domain of pitch measured by fundamental frequency, function-related domains of vocal quality, range, and habitual pitch level and the self-perceptions of transmasculine people during their first year of testosterone treatment. Method: Seven trans men received 2 voice assessments at baseline and 1 assessment at 3, 6, 9, and 12 months after starting treatment. Results: Vocal quality measures varied between and within participants but were generally within normal limits throughout the year. Mean fundamental frequency (MF0) during reading decreased, although to variable extents and rates. Phonation frequency range shifted down the scale, although it increased in some participants and decreased in others. Considering MF0 and phonation frequency range together in a measure of habitual pitch level revealed that the majority of participants spoke using an MF0 that was low within their range compared with cisgender norms. Although the trans men generally self-reported voice masculinization, it was not correlated with MF0, frequency range, or habitual pitch level at any time point or with MF0 note change from baseline to 1 year of testosterone treatment, but correlations should be interpreted with caution due to the heterogeneous responses of the 7 participants. Conclusion: In trans men, consideration of voice deepening in the context of objective and subjective measures of voice can reveal unique profiles and inform patient care.