Hibernoma is a rare benign tumour that was first described by Merkel in 1906. It arises from remnants of brown fat and has a differential diagnosis of lipoma and liposarcoma. This is a case report of a 31-year-old male with a slow-growing mass in the left flank that produced constant pain radiating to the groin. Computerised tomography localised the mass within the external oblique muscle, which showed some heterogeneity and low attenuation. The mass appeared hypodense to muscle on T1 and hyperdense to muscle on T2 weighted magnetic resonance images. Prominent vascularity of the mass was noted. Finally, the lesion was found to be a 'typical' hibernoma on core-needle biopsy. It was surgically resected with a cuff of muscle. He recovered without complication, and there is no clinical evidence of recurrence at 6 months.