Non-Hodgkin's lymphoma (NHL) is a rare tumor of the skull base. As the incidence of primary central nervous system (CNS) lymphoma has increased, atypical presentations involving the skull or cranial base exclusively have been reported. In immunocompetent patients with no previous history or predisposing factors, the diagnosis of primary NHL of the skull base may be delayed. We present four cases of nasal and paranasal sinus NHL with both skull base and intracranial involvement in immunocompetent patients. Clinicopathologic correlation suggests that cranial base and intracranial involvement with NHL represents advanced-stage primary sinonasal disease. Surgical biopsy before definitive treatment is recommended. Radiation therapy provides local control; adjuvant chemotherapy after primary radiation therapy may be required for recurrent disease.