A consensus has not yet been reached for the ideal moment to carry out pleurodesis in patients with malignant pleural effusion among the majority of centres, especially those which don’t specialise in oncologic treatment. The PET (positron emission tomography)/CT (computed tomography) used in the staging of patients with non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC) has caused controversy when used in the evaluation of therapeutical response and in detection of recurrence in patients with pleurodesis. For not distinguishing between inflammatory and neoplasic processes while using PET or CT, suspicion of pleural involvement can result in the indication for invasive diagnostic procedures or inadequate exchange of therapy. In such cases, the hypothesis of the inflammatory process must be included in the differential diagnoses for positive findings with the PET/CT in patients with NSCLC who have undergone pleurodesis, independently of time since the procedure. The reports of two patients with NSCLC have been presented in order to illustrate situations in which pleurodesis has been performed at the moment of diagnosis, outside of a cancer centre.