<b><i>Introduction:</i></b> Abnormal facial growth is a recognized outcome in cleft lip and palate (CLP), resulting in a concave profile and a class III occlusal status. Maxillary osteotomy (MO) is undertaken to correct this facial deformity, and the surgery can impact speech articulation, although the evidence remains limited and ill-defined for the CLP population. <b><i>Aims:</i></b> The aim of the study was to investigate the impact of MO on the production of the fricatives /f/ and /s/, using perceptual and acoustic analyses, and to explore the nature of speech changes. <b><i>Methods:</i></b> Twenty participants with CLP were seen 0–3 months pre-operatively (T1) and 3 months (T2) and 12 months (T3) after MO. A normal group (<i>N</i> = 20) was similarly recruited. Perceptual speech data was collected according to a validated framework and ratings made on audio and audio-video recordings (VIDRat). Spectral moments were centre of gravity (CG), standard deviation (SD), skewness (SK) and kurtosis (KU). Reliability studies were carried out for all speech analyses. <b><i>Results:</i></b> For the CLP group, VIDRat identified dentalization/interdentalization as the main type of pre-operative error for /s/ with a statistically significant improvement over time, χ<sup>2</sup>(2) = 6.889, <i>p</i> = 0.032. Effect sizes were medium between T1 and T3 (<i>d</i> = 0.631) and small between T2 and T3 (<i>d</i> = 0.194). For the acoustic data, effect sizes were similarly medium between T1 and T2 (e.g., SK, /f/ <i>d</i> = 0.579, /s/ <i>d</i> = 0.642) and small between T1 and T3 across all acoustic parameters. Independent <i>t</i> tests showed mainly statistically significant differences between both groups at all time points with large effect sizes (e.g., T2 CG, <i>t</i> = –4.571, <i>p</i> < 0.001, <i>d =</i>1.581), indicating that /s/ was not normalized post-operatively. For /f/, differences tended to be at T1 with large effect sizes (e.g., CG, <i>t</i> = –2.307, <i>p</i> = 0.028, <i>d</i> = 0.797), reflecting normalization. <b><i>Conclusions and Implications:</i></b> This is the first speech acoustic study on /f/ for individuals with CLP undergoing MO. The surgery has a positive impact on /f/ and /s/, which appear to stabilize 3 months post-operatively. Speech changes are an automatic and a direct consequence of the physical changes brought about by MO, effecting articulatory re-organization. The results of the study have direct clinical implications for the clinical care pathway for patients with CLP undergoing MO.