Although it is generally accepted that a malignant transient pleural transudate may appear during the early stages of lymphatic obstruction, cases demonstrating such probability are rare in literature. A 67-year-old woman was admitted to hospital because a lymphangitic carcinomatosis and a transudative infrapulmonary pleural effusion with a cytology positive for adenocarcinoma. One month later the effusion keeps being positive for adenocarcinoma but exudative in character. Lymphatic obstruction appears as the cause of the initial transudative characteristics of the pleural effusion.