We report the case of a 15-year-old girl who presented with a gradually enlarging subcutaneous mass in the left gluteal region. Magnetic resonance imaging (MRI) revealed a well-defined mass with a smooth margin. The lesion appeared homogenously hypointense on T1-weighted images, while T2-weighted images showed a lobulated structure with various signal intensities. On diffusion-weighted images, the lesion demonstrated markedly high signal intensities. These findings suggested an aggressive soft-tissue neoplasm. The patient underwent a total resection of the mass. The resected specimen was a lobulated mass covered with a fibrous capsule. The cut surface showed grayish white and partially contained black spots, which indicated pigmentation with melanin. Histopathological examination revealed that the tumor consisted of fibrous cellular stroma and lobules of follicular germinative cell nests, forming a structure known as a fibroepithelial unit. The tumor cells showed peripheral palisading arrangement. There were no atypical cells suggestive of malignancy. The final diagnosis was thus trichoblastoma, which is a rare benign cutaneous neoplasm that derives from germinative hair follicle cells. It usually arises in the face or neck of middle-aged or older adults, and its occurrence in the gluteal region of a young girl is thus unusual. On MRI, it may mimic an aggressive soft-tissue neoplasm.