Major salivary gland agenesis, a rare condition, may be asymptomatic or exhibit symptoms, such as dry mouth, dysphagia, and dental caries. Although uncommon, various ectodermal developmental syndromes associated with major salivary gland agenesis have been reported. Here, we report a patient who presented with a left submandibular triangle neck mass mimicking a salivary gland tumor, and received the final diagnosis of diffuse large B-cell lymphoma after excisional biopsy. Moreover, bilateral submandibular gland agenesis was incidentally detected during physical examination and image study. Though submandibular gland is the major structure in the submandibular triangle, its agenesis may occur even in nonsyndromic and nonxerostomic patients.