Purpose <p>This study aimed to evaluate tongue strength and endurance in patients with OSA and identify variables that modify their effects on OSA severity.</p> Methods <p>A cross-sectional study included 189 adults with OSA, classified according to the apnea-hypopnea index (AHI) as mild (<i>n</i> = 63), moderate (<i>n</i> = 52), or severe (<i>n</i> = 74). The anterior and posterior tongue strengths, and tongue endurance were measured using the IOPI^® Pro device. General linear models were applied to estimate unadjusted and adjusted marginal means. Adjustment was made for age, sex, and body mass index (BMI).</p> Results <p>The anterior tongue strength did not differ significantly across mild, moderate, and severe OSA (56.11 ± 11.31 vs. 51.32 ± 10.67 vs. 55.55 ± 13.22 kPa, <i>p</i> = 0.07), nor did posterior tongue strength (50.16 ± 16.14 vs. 46.25 ± 12.55 vs. 47.84 ± 13.39 kPa, <i>p</i> = 0.328), or tongue endurance (16.00 (12,22) vs. 14.75 (12,17.5) vs. 17.30 (13,23) seconds, <i>p</i> = 0.744). BMI was a significant effect modifier for anterior and posterior tongue strength. In the non-obese subgroup (BMI &lt; 30&#xa0;kg/m²) adjusted analyses for age and gender revealed differences in mean anterior (diff = 10.48, <i>p</i> = 0.017) and posterior (diff = 13.26, <i>p</i> = 0.02) tongue strength between patients with mild and severe OSA.</p> Conclusion <p>In an adult cohort, tongue strength did not differ among patients with mild, moderate, and severe OSA. However, in non-obese patients (BMI &lt; 30&#xa0;kg/m²), tongue strength was lower in those with severe OSA compared to those with mild OSA. Future studies on the impact of tongue strength may be best directed at non-obese patients with OSA.</p>