This chapter gives an overview and update on functional neurological disorder (FND), also known as dissociative neurological symptom disorder and previously known as conversion disorder. FND is the presence of neurological symptoms that are not explained or explainable by a neurological disorder. FND has been assumed to be a purely stress-related psychiatric disorder, but over the recent decades, this simplistic conception has been supplanted by more nuanced models of symptom generation. FND is no longer a diagnosis of exclusion. Instead, wherever possible, it is ruled-in by distinct features of history and examination, the latter known as positive clinical signs. There have been concurrent advances in the biological understanding of FND, exemplified by functional neuroimaging studies that have indicated that FND can be distinguished from, for example, feigned symptoms mimicking the disorder. FND encompasses multiple subtypes, from seizures to motor disorders to sensory abnormalities. Symptoms often co-occur, sometimes in a striking fashion.

Current treatment options for FND are limited, and many patients have severe long-term symptoms despite best-available treatment including psychological therapies and medication. Nevertheless, there are simple, and sometimes effective, steps that clinicians can take to manage and treat patients.