Chronic fatigue syndrome (CFS) or myalgic encephalomyelitis (ME) is characterised by persistent fatigue, which has a significant impact on functioning and is associated with other symptoms. Table 1 shows the characteristic features of the fatigue and the commonly associated symptoms. Post exertional malaise is a particularly useful symptom. Children will describe this as an increase in fatigue and symptoms after doing more than usual. For example, feeling too unwell to go to school on Thursday and Friday having been to school at the beginning of the week.