Acute pericarditis associated with lung cancer is a relatively frequent complication but is usually not symptomatic unless it causes tamponade. The clinical presentation is classically with dyspnea, thoracic pain, signs of right cardiac failure then left cardiac failure and syncope but it is often a difficult diagnosis in a patient with multi-symptomatic disease. The diagnosis is based on cardiac echography. Toxicity due to radiotherapy or more rarely an infectious etiology must be considered. Clinically significant effusions must be drained because of the high rate of recurrence after a simple aspiration. Drainage is formally indicated when, at echocardiography, the effusion exceeds 20mm in diastole, in cases of tamponade or in cases of compromised hemodynamic status. The formation of a pericardial window at thoracotomy prevents recurrences. Based on old, retrospective, very heterogeneous case series the prognosis, is generally considered to be poor with a median survival which does not exceed 100 days and a one year survival generally lower than 10%. Prognosis is better where diagnosis occurs at an earlier stage allowing regular follow-up and surgical intervention in a non-emergency setting.