OBJECTIVE Our goal was to assess the computed tomography (CT) imaging findings of thymoma and to correlate these features with Masaoka staging system and prognosis. METHODS CT findings of thymoma were analysed in 58 patients who had undergone surgery between January 2002 and September 2007. All cases were classified according to the Masaoka staging system. The presence of various CT findings was correlated with tumour invasiveness and recurrence. In statistical analysis, a p value <0.05 was interpreted as significant. RESULTS The study found 26 noninvasive thymomas and 32 invasive thymomas. Invasive thymomas were more likely to be greater in size (p<0.01), with lobulated or irregular contours (p<0.02), a necrotic or cystic component (p<0.04), foci of calcification (p<0.05) and heterogeneous contrast enhancement (p<0.01) than were noninvasive thymomas. Disease progression developed in nine of 58 patients. Tumour recurrence and metastasis correlated with greater size (p<0.04), lobulated or irregular contours (p<0.01), complete mediastinal fat obliteration (p<0.01), great vessel invasion (p<0.01) and pleural implants (p<0.02). CONCLUSIONS CT is useful in differentiating invasive from noninvasive thymomas and plays an important role in evaluating and treating these patients for multimodal therapy with neoadjuvant approaches. Moreover, CT findings may serve as predictors of postoperative recurrence or metastasis.