Solitary fibrous tumor of the pleura (SFTP) is a rare tumor. The prognosis is relatively good, but up to 20% of the cases are malignant. We presented a case of a large mass of the thorax, showing malignant poor prognosis features. A 73-year-old male, former smoker, presented with a history of dry cough. Chest CT revealed a left bronchopulmonary mass (11 cm × 14 cm) extending from the costal pleura to the left hilum. Histopathologic examination of the transbronchial lung biopsy was consistent with SFTP. A left pneumonectomy was performed due to invasive nature of the lesion. According to features associated to poor prognosis (lung tumor ≥ 10 cm, hipercellularity, abundant intratumor blood vessels and areas of necrosis), and in spite of proliferation index (Ki67+) <1%, the case was discussed in a multidisciplinary meeting, and was assumed to be malignant. At the present time, the patient is his fifth month after surgery, in tight follow up. This case highlights a rare SFTP presenting bad prognosis features, that although completely resected should have long-term follow-up due to the high risk of recurrence.