Hibernoma is an uncommon benign, slow-growing soft-tissue tumor mainly consisting of brown fat. It is commonly seen in back, especially around the inter-scapular, neck, axillae, thigh, and intra-thoracic area. Complete excision is the only curative modality of hibernoma. No report of metastases or malignant transformation of the hibernoma has been published before. We report a 40- year-old man with a 5cm painful well-defined movable mass of 1-month duration on the right flank. He experienced tenderness on the skin lesion for 2 weeks. A incisional biopsy of mass was taken. Histopathological examination of the incisional biopsy revealed a lipoma. An elective surgery was performed and the mass was completely excised. Histopathological examination of the excision revealed the pale stained multi-vacuolated brown fat cells with abundant mature adipose cells consistent with a hibernoma. In 9 months follow up, the patient was asymptomatic without any recurrence. This report presents a case of a hibernoma of the right flank that was initially diagnosed as a lipoma at incisional biopsy, and subsequently investigated at complete excision. The clinical presentation of a hibernoma be similar to lipoma, and pathologic finding of the biopsy of hibernoma can considered a lipoma when biopsy could not include whole lesion.