BACKGROUND Pseudochylothorax is a rare entity, with only a few hundred case reports worldwide. It presents as a pleural effusion rich in lipids, typically with a cloudy, milky appearance. The diagnosis is made based on the levels of cholesterol and triglycerides in the pleural fluid. CASE REPORT This is the case report of a 55-year-old woman with a history of pleuropulmonary tuberculosis that was treated in childhood, with a new infection and treatment in adulthood that evolved to a left pleural effusion. Thirteen years after completing her last treatment for tuberculosis, the patient developed general fatigue and dyspnea on exertion. Computed tomography of the chest confirmed the presence of a pleural collection in the same location as in adolescence, suggesting a chronic evolution with encystation. The patient underwent ultrasound-guided diagnostic thoracentesis. The collected liquid was thick, chocolate-colored, with the following biochemical characteristics: pH, 7.3; glucose, 37.9 mg/dL; LDL, 2059.8 IU/L; total protein, 8.8 mg/dL; triglycerides, 90 mg/dL; adenosine deaminase, 56 U/L; and cholesterol, 300 mg/dL. The effusion was characterized as a pseudochylothorax. The cell count showed 631 000 leukocytes/µL, with 87.9% polymorphonuclear cells. Owing to the patient's respiratory symptoms, an evacuatory thoracentesis was performed. After the procedure, the patient's symptoms improved. CONCLUSIONS Although pseudochylothorax is a rare condition, its possibility must always be kept in mind to avoid the hazards of misdiagnosis. In addition to the 'classic' milky and machine oil appearance, a chocolate-colored appearance should also serve as a clue to the diagnosis of pseudochylothorax.