Polymorphous low-grade adenocarcinoma is a malignant epithelial tumour with low metastatic rate and infiltrative growth pattern. The palate is the most common site. Paranasal sinuses are uncommon venues for polymorphous low-grade adenocarcinoma. Here, we report a polymorphous low-grade adenocarcinoma case of the maxillary sinus, a very rare location. Although it is a low grade malignancy, progression may develop after a long time. Therefore, polymorphous low-grade adenocarcinoma should be kept in mind in the differential diagnosis even in rare sites in the head and neck.