Sinonasal malignancies are rare head and neck cancers. We present three patients with sinonasal adenocarcinomas that have different characteristics. The first patient was asymptomatic, and the nasoendoscopy revealed a nasopharyngeal mass. He was diagnosed with stage I papillary type adenocarcinoma and was treated with nasal endoscopic surgery, with no evidence of tumour recurrence for one year. In the second case, the patient had a unilateral nasal blockage with blood-stained nasal discharge. Nasoendoscopy showed a septal mass. The patient was diagnosed with stage II low-grade non-intestinal sinonasal adenocarcinoma (NITAC) and underwent two nasal endoscopic surgeries with no tumour recurrence after six months. In the third case, the patient reported ear fullness, blood-stained nasal discharges, and painless neck swelling. Nasoendoscopy showed a right septal mass, and he was diagnosed with stage IVc high-grade NITAC. He received concurrent chemoradiotherapy and is doing well three months after treatment completion.