Objective/hypothesis: The aim of the study was to measure the morphology of the epilaryngeal tube during sustained phonation as a function of loudness variation and to compare subjects of different genders. Study design: This is a prospective study. Methods: Five female and five male classically trained singers were recorded by magnetic resonance imaging with simultaneous audio recordings while sustaining phonation at three different loudness conditions. Three-dimensional subsections of the vocal tract were segmented on multi-image-based cross-sections. Different volume and area measures were determined and their relation to sound pressure level and loudness condition was analyzed. Results: Male singers tended to narrow the epilaryngeal tube when increasing sound pressure level whereas female singers did not. Conclusion: Strategies of vocal tract adjustments during loudness variation in classical singing appear to be gender specific.