Aim: Somatoform disorders are common and often chronic. It would be helpful to distinguish those patients who are likely to have a positive treatment course from those who are likely to follow a negative course. Such studies of different somatoform disorders are scarce, especially in secondary psychiatric care. This study examined the 6-month treatment course of psychological, physical symptoms, and functioning, and its predictors in a naturalistic sample of secondary psychiatric care outpatients with somatoform disorders. Method: The present study used routine outcome monitoring data of patients with somatoform disorders regarding their 6-month treatment course of psychological and physical symptoms as well as functioning. The following patient groups were included: total group of somatoform disorders (N = 435), and undifferentiated somatoform disorder (N = 242), pain disorder (N = 102), body dysmorphic disorder (N = 51), and hypochondriasis (N = 40). Measures were Mini-International Neuropsychiatric Interview plus, Brief Symptom Inventory, Montgomery–Ǻsberg Depression Rating Scale, Brief Anxiety Scale, Short Form Health Survey 36, and Physical Symptom Checklist (PSC). Results: The study population generally showed high co-morbidity, especially with anxiety and mood disorders. The PSC total score, body dysmorphic disorder, and hypochondriasis were significant predictors for the treatment course of symptoms (Brief Symptom Inventory), whereas the PSC total score was the only significant predictor for the course of functioning (Short Form Health Survey 36). Conclusion: Secondary psychiatric care outpatients with somatoform disorders showed high co-morbidity with anxiety and mood disorders, and an unfavourable 6-month course of both symptoms and functioning. Clinical implications are discussed, such as additional treatment of co-morbidity in somatoform disorders.