(CDE) working group. The second step in this process, as recommended by the NIH/CDC CDE working group, involves assembling information from various sources to confirm the presence of PEM. There have not been any efforts, to date, to standardize this second-step process in the assessment of PEM. The current study examined whether five supplementary items on the DSQ could be used to operationalize the second step of the recommendations made by the NIH/CDC CDE working group. The five supplementary DSQ PEM duration items correctly categorized patients with ME or CFS 81.7% of the time, while incorrectly categorizing multiple sclerosis (MS) and post-polio syndrome (PPS) as ME or CFS only 16.6% of the time. The findings suggested that a PEM second-step process could be operationalized using supplementary DSQ items.