CONTEXT: Positive airway pressure (PAP) is the first-line therapy for obstructive sleep apnea (OSA). Overnight PAP titration for determining optimal PAP requirements is expensive and often inconvenient. Prediction of optimal PAP requirements from diagnostic polysomnography via mathematical equations is possible but variable across populations. AIMS: We aimed to (1) determine the optimal PAP requirement, (2) determine differences in optimal PAP requirements across OSA severity groups, (3) determine the relationship between optimal PAP requirement and diagnostic polysomnography measurements of OSA severity, and (4) develop a pilot equation to predict the optimal PAP requirement from diagnostic polysomnography in a sample from the Saudi population. METHODS: We analyzed records pertaining to adult OSA patients ( n = 215; 63% of males) who underwent standardized diagnostic and titration polysomnography in our sleep laboratory between 2015 and 2019. Demographic, anthropometric, and clinical information were also collected for the analysis. Inferential statistics were performed for comparisons between diagnostic and titration studies and between OSA severity groups. Regression analyses were also performed to determine the potential predictors of optimal PAP requirements. Data were presented as the mean (± standard deviation) or median (25 th –75 th quartiles) according to normality. RESULTS: The median optimal PAP requirement was 13 (9–17) cmH 2 O. The optimal PAP requirement was significantly greater for male versus female participants (14 [10–17] vs. 12 [8–16] cmH 2 O) and for participants with severe OSA (16 [12–20] cmH 2 O, n = 119) versus those with moderate (11 [8–14] cmH 2 O, n = 63) or mild (9 [7–12] cmH 2 O, n = 33) OSA. When combined, nadir oxygen saturation, oxygen desaturation index, and arousal index could be used to predict the optimal PAP requirement ( R 2 = 0.39, F = 34.0, P < 0.001). CONCLUSIONS: The optimal PAP requirement in the Saudi population is relatively high and directly correlated with OSA severity. Diagnostic polysomnography measurements of OSA severity predicted the optimal PAP requirement in this sample. Prospective validation is warranted.