Context: Down syndrome is a genetic condition caused by trisomy 21, often accompanied by orofacial hypotonia and anomalies in stomatognathic development. A hypotonic tongue may alter oral cavity morphology, particularly palatal depth, anterior dental relationships, and lip competence, thereby affecting mastication, swallowing, and speech. Aims: To evaluate the association between tongue strength and endurance with oral cavity morphology in children with Down syndrome during the permanent dentition period. Settings and Design: A cross-sectional analytic study was conducted among children with Down syndrome at RCDS POTADS, Jakarta. Materials and Methods: Thirty-three children aged 15–18 years participated in this study. Tongue strength and endurance were measured using a TongueMeter™, while oral cavity morphology was measured linearly for palatal depth, overjet, overbite, and lip competence. Statistical Analysis: Pearson correlation and multiple linear regression analysis were performed to determine the relationship between tongue strength and endurance with oral cavity morphology. Results: Tongue strength showed a significant negative correlation with palatal depth (r = −0.359; P = 0.040). Linear regression confirmed that tongue strength significantly influenced palatal depth (β = −0.364; B = −0.679; R 2 = 0.133; P = 0.037). Tongue endurance showed no significant association with palatal depth, overjet, overbite, or lip competence. Conclusions: Tongue strength may play a determining role in shaping palatal depth in children with Down syndrome during the permanent dentition period, whereas tongue endurance showed no significant effect. The ideal positioning and function of the tongue contribute to the harmonious development of oral morphological components, facilitating the establishment of a proper occlusal relationship. In children with Down syndrome who exhibit hypotonia, this study demonstrated that lower tongue strength is associated with a deeper palatal morphology. © 2026 Journal of Indian Society of Pedodontics and Preventive Dentistry.