This report summarizes findings related to the psychometric properties (internal consistency and construct validity) of the Pittsburgh Sleep Quality Index (PSQI) and discusses issues related to its use based on data from two clinical studies with diverse samples of cancer patients. Subjects completed a questionnaire that included the PSQI, the Schwartz Cancer Fatigue Scale, and specific demographic, disease, and treatment variables. There were complete data on 170 (of 214) cases in Study 1 and 249 (of 259) cases in Study 2. The Cronbach's alpha for the Global Sleep Quality scale was 0.81 in Study 1 and 0.77 in Study 2 A comparison of Global Sleep Quality in two contrasting groups with low and high fatigue yielded statistically significant differences in both samples. Psychometric evaluation supports its internal consistency reliability and construct validity. However, the scoring is rather cumbersome and raises questions regarding level of measurement and appropriate analysis techniques.