Summary: Objectives: Lip trills are widely used as a voice warm-up technique among singers. However, little is known about the effects of lip trills in cases of voice disorders. We examined the therapeutic effects of lip trills in patients with glottal gap. Methods: Patients with glottal gap were classified into three groups according to the type of gap: gap-only, gap with muscle tension dysphonia (MTD), and a sulcus vocalis group. Patients underwent perceptual, acoustic/aerodynamic analyses, stroboscopic evaluations, and subjective analyses using a questionnaire before and after lip trills. The results were analyzed before and after trills and according to and between the groups. Results: The results in 42 patients were analyzed. Most of the parameters were improved and glottal gap was significantly reduced after trills in all patients. In the gap-only group (n = 19), most of the parameters showed improvement and were within the respective normal ranges, and glottal gap was improved after trills. In the MTD group (n = 13), although many parameters were improved, the improvement was not as prominent as in the gap-only group. In the sulcus vocalis group (n = 10), only some of the parameters were improved and the improvement in glottal gap was limited. Conclusions: Lip trills were an effective treatment for glottal gap. The therapeutic effect was prominent in the gap-only group, followed by the MTD and sulcus vocalis groups. Trills can be used as an adjuvant treatment option in voice therapy in cases of various voice disorders.