Objective: To study the course of medically unexplained symptoms (MUS), somatisation disorder, and hypochondriasis, and related prognostic factors. Knowledge of prognostic factors in patients presenting persistent MUS might improve our understanding of the naturalistic course and the identification of patients with a high risk of a chronic course. Methods: A comprehensive search of Medline, PsycInfo, CINAHL, and EMBASE was performed to select studies focusing on patients with MUS, somatisation disorder, and hypochondriasis, and assessing prognostic factors. Studies focusing on patients with single-symptom unexplained disorder or distinctive functional somatic syndromes were excluded. A best-evidence synthesis for the interpretation of results was used. Results: Only six studies on MUS, six studies on hypochondriasis, and one study on abridged somatisation could be included. Approximately 50% to 75% of the patients with MUS improve, whereas 10% to 30% of patients with MUS deteriorate. In patients with hypochondriasis, recovery rates vary between 30% and 50%. In studies on MUS and hypochondriasis, we found some evidence that the number of somatic symptoms at baseline influences the course of these conditions. Furthermore, the seriousness of the condition at baseline seemed to influence the prognosis. Comorbid anxiety and depression do not seem to predict the course of hypochondriasis. Conclusions: Due to the limited numbers of studies and their high heterogeneity, there is a lack of rigorous empirical evidence to identify relevant prognostic factors in patients presenting persistent MUS. However, it seems that a more serious condition at baseline is associated with a worse outcome.