Extrapleural lipomatosis refers to the abnormal accumulation of adipose tissue within the extrapleural space. This condition may coexist with mediastinal fat expansion and is often associated with excessive endogenous or exogenous corticosteroid exposure. Diagnosis is typically established radiologically, characterized by fat-attenuated pleural thickening that may appear diffuse or irregular on imaging. Clinically, patients may present with dyspnea or respiratory discomfort, reflecting restricted lung expansion secondary to excess extrapleural fat, findings that can mimic restrictive lung disease. Management depends on disease severity and underlying cause. Observation is appropriate for mild or asymptomatic cases, while weight reduction and control of glucocorticoid excess are mainstays of conservative treatment. Surgical intervention is rarely required and reserved for symptomatic cases due to significant lung compression. This chapter provides an overview of the pathophysiology, diagnosis, management, and prognosis of extrapleural lipomatosis.