Vocal cord dysfunction (VCD) is an uncommon condition which often mimics asthma in presentation and severity. We present nine- and 11-year-old female siblings with vocal cord dysfunction, which is a dysfunction of the larynx involving unintentional paradoxical adduction of the vocal cords during inspiration. We evaluated the use of exercise testing in conjunction with pulmonary function testing in suspected vocal cord dysfunction. Although normal pulmonology function tests were elicited with the patient at rest, exercise testing revealed blunting of the expiratory loop with attenuation of the inspiratory loop unique to VCD. The child underwent video laryngoscopy in the specialised voice clinic, which confirmed vocal cord dysfunction. Exercise testing is a rapid and noninvasive means of diagnosing vocal cord dysfunction in a small subset of patients, but video laryngoscopy, with training manoeuvres to elicit paradoxical vocal cord movements in VCD, remains the gold standard of diagnosis of VCD.