This review appraises the process of development and the measurement properties of the Pittsburgh sleep quality index (PSQI), gauging its potential as a screening tool for sleep dysfunction in non-clinical and clinical samples; it also compares non-clinical and clinical populations in terms of PSQI scores. MEDLINE, Embase, PsycINFO, and HAPI databases were searched. Critical appraisal of studies of measurement properties was performed using COSMIN. Of 37 reviewed studies, 22 examined construct validity, 19 - known-group validity, 15 - internal consistency, and three - test-retest reliability. Study quality ranged from poor to excellent, with the majority designated fair. Internal consistency, based on Cronbach's alpha, was good. Discrepancies were observed in factor analytic studies. In non-clinical and clinical samples with known differences in sleep quality, the PSQI global scores and all subscale scores, with the exception of sleep disturbance, differed significantly. The best evidence synthesis for the PSQI showed strong reliability and validity, and moderate structural validity in a variety of samples, suggesting the tool fulfills its intended utility. A taxonometric analysis can contribute to better understanding of sleep dysfunction as either a dichotomous or continuous construct