This study investigates the relationship between glottal gap and vocal function in patients with glottic incompetence dysphonia. Twenty patients with vocal fold paralysis (VFP), 17 patients with vocal fold atrophy (VFA), and five patients with sulcus vocalis (SV) were examined. Glottal gap area at the most closed point of vibration was measured using digitized videostroboscopic images. Glottal gap area was correlated with acoustic and aerodynamic measures of vocal function. Patients with VFP had the largest glottal gaps and had significantly worse vocal function than did the patients with VFA or SV. Regardless of groups, however, where glottal gap size was similar, there was no difference in vocal function. Therefore vocal function was mainly influenced by glottal gap size, not by whether glottic incompetence was the result of VFP, VFA, or SV.