A 46-year-old asymptomatic male was detected to have a posterior mediastinal mass on a routine check-up. He underwent thoracotomy to remove the mass, which was found to be a hibernoma. The mediastinum is an extremely rare site for an even rarer tumor like the hibernoma. An additional unique feature was the very large tumor size despite which the patient was asymptomatic. Imaging studies are not helpful in revealing its clinically indeterminate nature, hence a surgical specimen is necessary to establish the correct diagnosis. Total excision is advocated for cure, as there is no known malignant potential.