Epithelial thymic tumours (ETT), which comprise the majority of thymomas, are neoplasias developed from the epithelial cells of the thymus and constitute around 30% of anterior mediastinal masses in adults. Thymomas consist of cells with no cytological characteristics of malignity; malignant behaviour is determined by invasion of the capsule and adjacent structures. These tumours present a broad spectrum of clinical and morphological characteristics and the small series of known patients makes establishing a standard treatment difficult.A retrospective study was made into thymoma diagnosed patients admitted to the Portuguese Oncology Institute in Porto (IPO-Porto) from 1983 to 2004. Clinical characteristics were analysed and a histological classification made in accordance with World Health Organization criteria, Masaoka staging, and their relation to treatment methods. A review of the clinical records of these patients was then made, as well as a review of histological material for classification in line with 1999 WHO criteria.Twenty-eight ETT patients were treated at the IPO-Porto between 1983 and 2004. Of these, 21 had invasive thymomas and these are the subject of this study. Eleven subjects were male and 10 female, with a median age of 55 years (24-79 years). The WHO histological classification was as follows: 2 patients (9.5%) type A, 6 (28.6%) type AB, 4 (19%) type B1, 2 (9.5%) type B2, 7 (33.4%) type B3. Masaoka staging was 9 patients (42.8%) with stage II, 6 (28.6%) with stage III and 6 (28.6%) with stage IVa. The majority of patients had local symptoms, with only one subject diagnosed with erythrocyte aplasia and five with Myasthenia Gravis (MG). The 6 patients who were given complete surgical resection only showed no evidence of disease recurrence (2 type A-II, 2 type AB-II, 1 type B1-II, 1 type B2- IVa), with follow-up from 8-144 months. Ten patients with complete resection received adjuvant treatment; 6 radiotherapy (4 B3-II patients, 2 B3-III patients), 2 chemotherapy (AB-IVa) and 2 chemo and radiotherapy (B1-IVa, B2-III). Only the 2 patients who underwent adjuvant chemotherapy relapsed, at 168 and 46 months, dying at 168 and 49 months, respectively. The remaining patients who were given adjuvant treatment did not present signs of disease. Of the 5 subjects having incomplete resection followed by complementary treatment (2 AB-III patients, 2 B1-IVa patients, 1 B3-III patient), 3 died, at 11 months (B3-III), 12 months (B1-IVa) and 241 months (AB-III), the latter with MG.Predictive factors of bad prognosis here were incomplete resection, advanced staging and B3 histological subtype, the smallness of this series notwithstanding. It is necessary to investigate the role of adjuvant and neoadjuvant treatment in a group of subjects with advanced disease of the B3 histological subtype.