In the Finnish medical discussion during the middle decades of the twentieth century, the challenging differential diagnostics between hyperthyroidism and various neuroses was perceived to yield a risk of unnecessary surgical interventions of psychiatric patients. In 1963, the Finnish surgeon Erkki Saarenmaa claimed that ‘the most significant mark of a neurotic was a transverse scar on the neck’, a result of an unnecessary thyroid surgery. The utterance was connected to the complex nature of thyroid diseases, which seemed to be to ‘a great extent psychosomatic’. Setting forth from this statement, the article aims to decipher the connection between hyperthyroidism, unnecessary surgical treatment and the psychosomatic approach in Finnish medicine. Utilising a wide variety of published medical research and discussion in specialist journals, the article examines the theoretical debate around troublesome diagnostics of functional complaints. It focuses on the introduction of new medical ideas, namely the concepts of ‘psychosomatics’ and ‘stress’. In the process, the article aims to unveil a definition of psychosomatic illness that places it on a continuum between psychological and somatic illness. That psychosomatic approach creates a space with interpretative potential can be applied to the historiography of psychosomatic phenomena more generally. Further inquiry into the intersections of surgery and psychosomatics would enrich both historiographies. It is also argued that the historical study of psychosomatic syndromes may become skewed, if the term ‘psychosomatic’ is from the outset taken to signify something that is all in the mind.