Nickel is the most common contact allergen affecting females in Europe and the USA. Nickel-containing metal alloys are extensively used for dental prostheses and orthodontic appliances. The aim of this study was to elucidate whether nickel sensitive persons are at greater risk of developing discomfort in the oral cavity during orthodontic treatment. Data from 1085 consecutive girls in active orthodontic treatment or in retention were collected by means of a questionnaire. No nickel allergic reaction on the oral mucosa was found. The majority of the girls with unspecific mucosal reactions and skin lesions were atopics with a chronic dermatitis. The findings do not indicate that nickel sensitive persons are at greater risk of developing discomfort in the oral cavity when wearing an intraoral orthodontic appliance.