There are limited published data on maximum mouth opening (MMO) for children with cleft lip or palate (CLP) or craniofacial anomalies (CFA). To report MMO of patients with CLP or CFA compared with non-affected controls. Retrospective cross-sectional review of electronic medical and dental records. Patients with CLP or CFA with recorded MMO, height, and weight were included and compared with a non-affected control individuals seen during orthodontic screening. Outcome measures included MMO, recorded in millimeters of inter-incisal distance, age, height, weight, and sex. Patients with CLP or CFA (n = 376) were matched by age and body mass standardized index (BMIz) to the non-affected pool (n = 376). The affected group had a MMO of 43.14 mm (±7.1 mm) compared with the control group MMO of 48.01 mm (±7.6 mm) with a statistically significant difference of -4.86 mm (p < .0001). Specifically, MMO of the unilateral cleft group is 4.26 mm smaller than that of non-affected controls (p < .0001). MMO of the bilateral cleft group is 3.65 mm smaller than that of non-affected controls (p = 0.0063). MMO for patients with CLP was significantly smaller as compared to non-affected controls. This study helps establish MMO values for children with CLP and CFA.