To review the evidence for overlap in the phenomenology of the Functional Somatic Syndromes (FSS). The FSS show considerable comorbidity, leading some to suggest they may be aspects of the same disorder.
We conducted a selective review of peer-reviewed articles on the co-occurrence of FSS symptoms and diagnoses.
Considerable evidence of overlap was found at the level of symptoms, diagnostic criteria, and clinical diagnoses made.
Phenomenological commonalities support a close relationship between the FSS, although differences remain in other domains. Whether the FSS may best be considered the same or different will depend on the pragmatics of diagnosis.