Patients commonly present in primary care with symptoms for which no physical pathology can be found. This study is a review of published research on medically unexplained symptoms (MUPS) in primary care. A literature review and qualitative comparison of information was carried out. Four questions were addressed: what is the prevalence of MUPS; to what extent do MUPS overlap with psychiatric disorder; which psychological processes are important in patients with MUPS; and what interventions are beneficial? Neither somatised mental distress nor somatisation disorders, based on symptom counts, adequately account for most patients seen with MUPS. There is substantial overlap between different symptoms and syndromes, suggesting they have much in common. Patients with MUPS may best be viewed as having complex adaptive systems in which cognitive and physiological processes interact with each other and with their environment. Cognitive behavioural therapy and antidepressant drugs are both effective treatments, but their effects may be greatest when the patient feels empowered by their doctor to tackle their problem.