Background <p>Seborrheic keratosis is a common benign epidermal neoplasm, typically arising on the trunk, face, and extremities. Auricular involvement is rare, and posterior auricular presentation is particularly uncommon, with few cases reported.</p> Case presentation <p>We describe a 68-year-old Iranian woman presenting with a 3 cm × 2 cm posterior auricular mass that had slowly enlarged over 5 years. The lesion was firm, nontender, and fixed to underlying tissue, raising concern for malignancy. A preoperative biopsy was performed, and histopathology confirmed seborrheic keratosis. Given the lesion’s size and atypical location, complete surgical excision was undertaken. Reconstruction of the resulting defect was achieved using a bilobed flap, executed in seven operative steps, utilizing mastoid and lateral neck skin to provide tension-free closure while preserving the retroauricular sulcus. Microscopic evaluation revealed acanthosis, papillomatosis, hyperkeratosis, and horn cysts without evidence of atypia or malignant transformation. The postoperative course was uneventful, with no complications or recurrence observed at 3-month follow-up. Both aesthetic and functional outcomes were satisfactory.</p> Conclusion <p>This case highlights the rarity of posterior auricular seborrheic keratosis and underscores the importance of histopathological confirmation in lesions with indeterminate clinical features. The bilobed flap provided reliable coverage for a relatively large auricular defect, achieving favorable cosmetic and functional results. Documentation of such uncommon cases contributes to improved diagnostic accuracy and supports evidence-based surgical management of auricular tumors.</p>