The congenital absence off the major salivary glands is a very infrequent disorder, in which several glands are usually involved at the same time. Sometimes this disorder can be associated with other developmental anomalies. The unilateral aplasia of the submandibular gland is an extremely rare finding with only 14 cases reported in the literature. Clinically, this kind of patients may complain of dryness of the mouth, difficulties in chewing and swallowing, severe periodontal disease or multiple caries, but usually they follow an asymptomatic course. Salivary gland aplasia can be diagnosed with a large variety off imaging techniques, which include computer tomography (CT), magnetic resonance imaging (MRR), ultrasonography (UUS), sialography, or scintigraphy. In this paper we report a case off a patient referred to our department with a long term and progressive growing neck mass, who has an unilateral submandibular gland aplasia associated to an ipsilateral hypertrophy off the sublingual gland. © Medicina Oral S. L.