Lymphadenopathy may be caused due to various reasons, most common being infections, neoplasms and immunologic disorders. Considering the frequent use of biomaterials in dentistry, it is not uncommon to find allergic reactions in the oral mucosa. Delayed-type hypersensitivity is one mechanism of allergy, which may manifest as either contact stomatitis or rarely present as only lymphadenopathy. An unusual case of unilateral submandibular gland swelling with associated lymphadenopathy during orthodontic treatment is reported. The processes followed in the differential diagnosis of the condition have been elucidated. Delayed hypersensitivity as a possible causative factor has been discussed. The article highlights the possibility of such conditions manifesting at any time during orthodontic therapy.