<p>The Pittsburgh Sleep Quality Index (PSQI) is widely used, but can be impractical in large studies due to its length. The two-item version (PSQI-2) is a promising alternative, with underexplored longitudinal properties in older adults. We evaluated its validity against the full PSQI in the MrOS Sleep Study cohort of older men. Cross-sectional validity (Bland-Altman, ROC curves for PSQI &gt; 5) and longitudinal properties (ICC, change score correlation, accuracy for ΔPSQI &gt; 3) were assessed. The PSQI-2 showed a strong cross-sectional association with the full PSQI (b = 2.167, p &lt; 0.001), explaining 72% of its variance. For identifying poor sleep quality, the PSQI-2 demonstrated excellent accuracy (AUC = 0.89) with an optimal cutoff of ≥2 (sensitivity=77.5%, specificity=84.5%). Longitudinally, both instruments showed moderate test-retest reliability (PSQI-2 ICC = 0.579; PSQI ICC = 0.639). The correlation between their change scores was strong (r = 0.682, p &lt; 0.001), and the PSQI-2 showed reasonable accuracy (AUC = 0.754) in detecting clinically meaningful change (Δ PSQI &gt; 3). The PSQI-2 is a valid and reliable tool for cross-sectional screening of poor sleep quality in older men at the cutoff of ≥2. It is also responsive to directional change over time and can identify individuals with clinically significant changes in sleep.</p>