Synchronous tumors are described as multiple primary malignancies presenting within 6 months of diagnosis of index tumors. Synchronous tumors of the lung and the head and neck region is frequently seen. However, isolated sphenoid sinus and lung cancers are not reported yet. Here, we reported an incidentally diagnosed simultaneous second primary sphenoid sinus tumor in a patient with lung cancer. Radiological evaluation results demonstrated a significant contrast-enhanced mass in the sphenoid sinus extending through the nasopharynx because of the destruction of the sphenoid sinus. The decision was made to proceed with chemotherapy and radiotherapy treatment regimens for the sphenoid sinus lesion, and right lobectomy was performed for the lung lesion. Asymptomatic simultaneous, synchronous, or metastatic tumors must always be kept in mind, and histopathologic diagnosis should be done for both tumors because presence of second tumor anywhere may change the treatment modality.