A 34-year-old patient had had Crohn's disease (CD) for eight years; she was seen for complaints of thoracic pain and fever, without gastrointestinal manifestations. Initial laboratory exams were compatible with the presence of inflammatory activity (VHS = 45 mm for normal value of 20 mm and PCR+). The physical exam revealed signs of pleural effusion in the left hemithorax base, which was confirmed by thoracic RX. The pleural liquid analysis showed that the cells were 100% of lymphocytes, with negative BAAR research. The pleural biopsy evidenced non caseous granuloma. Despite the tuberculosis treatment, the patient only got better when corticotherapy was introduced in high doses, suggesting the activity of CD as the cause of the pleural effusion. This case establishes a connection between activity of CD and manifestations of lung disease.