OBJECTIVES: Fatigue experienced by cancer patients need to be assessed carefully. Yet, there is no agreement on the most appropriate recall period to use. In this study, we compared responses to identical fatigue item pairs, varying only the reporting period (past 7-days versus past 4-weeks), and explored factors that influenced patients’ responses. METHODS: Sample included 216 cancer patients (63.5% female, 80.5% white, mean age=57.6; 36% had breast cancer). Patients were asked to complete either a 7-day (n=100) or 4-week (n=116) version of the Functional Assessment of Chronic Illness Therapy-Fatigue.  Cochran-Mantel-Haenszel statistics (CMH) and Cochran-Armitage trend tests were used to assess the association between time frame and item scores.  Information function curves at both item and scale levels were depicted to evaluate the precision along the fatigue continuum. Differential item functioning (DIF) was used to examine the psychometric stability between time frames. RESULTS: These two sample groups had comparable degree of fatigue severity at the time of survey (p=.209) and at the end of survey (p=0.074), as measured with a single 0-10 rating. No item was rejected by CMH or trend tests at p <0.01, indicating that time frame did not influence patients’ responses. Similarly, item information curves did not clearly favor either time frame. No item demonstrated DIF between time frames. Results of chi-square statistics showed that both gender and fatigue severity were not significantly associated with the time frame patients reported using to endorse items, p = 0.48 and p = 0.33, respectively. CONCLUSIONS: This study suggests the 7-day and 4-week time frame are equally appropriate in measuring fatigue. Slight preference might be given to the more informative 7-day reporting period. However, substantive considerations regarding the appropriate time frame should outweigh statistical ones. Comparison of the 7-day time frame to shorter ones (e.g., 24 hour) is needed.