OBJECTIVES: This study evaluated the effects of orthognathic surgery on speech of Class III ('underbite') patients with repaired cleft lip and palate (CLP) through ultrasound imaging, aerodynamic assessment and articulatory analyses before and after surgery to evaluate how surgery impacts articulation, velopharyngeal (VP) function and hypernasality. MATERIALS AND METHODS: Tongue gestures of five Class III patients with repaired CLP, five Class III patients without CLP and five Class I controls were visualised through ultrasound imaging pre- and post-surgery. Tongue Dorsum Excursion Index and Tongue Constraint Position Index (TCPI) were calculated using ultrasound, and VP insufficiency (VPI) indices were measured using pressure flow assessment and compared with qualitative-perceptual ratings by Speech-Language Pathologists (SLPs). Linear mixed-effects models were used to test for significant post-operative changes in Dorsum Excursion Index and TCPI among consonants. Pressure flow measures are expected to estimate VP gap size during speech using PERCI-SARS. RESULTS: Patients with CLP had significantly lower Dorsum Excursion Index for /k/ before front (p = 0.001) and back vowels (p < 0.001). TCPI revealed consistently lower values for patients with CLP than controls and Class III patients, with inter- and intra-speaker variation for all consonants. Pressure flow data of two patients with CLP showed evidence of VPI and altered nasality post-surgery. CONCLUSION: Patients with CLP present with lower Dorsum Excursion Index and TCPI when compared to controls, suggesting more anterior tongue positioning. Dorsum Excursion Index and TCPI can be used to understand tongue shape and movement changes, potentially elucidating functional effects of jaw surgery on speech. Dorsum Excursion Index and pressure flow data indicate increased compensatory articulations and VPI after orthognathic surgery for patients with CLP, impacting speech.