Dysfunctional breathing is a group of respiratory disorders that cause dyspnea, with no organic cause, or that are disproportionate to the organ involvement. Hyperventilation syndrome is the best-known manifestation of dysfunctional breathing. It is very often associated or secondary to anxiety disorders. When the diagnosis of dysfunctional breathing is not considered, it can lead to multiple and unnecessary investigations, further increasing anxiety. The diagnosis is based on various tests, none of which is really specific, and remains based on a bundle of arguments. Management must be adapted for each patient and is based on respiratory rehabilitation techniques.