Background: The presence of pectus excavatum(PEX) has been occasionally associated with pericardial effusion. Aim of the present study was to compare incidence and prognosis of pericardial effusion in a group of unselected patients with PEX vs a control group. Methods: From a prospective registry of consecutive patients who underwent chest CT for cardiovascular disease, subjects with a radiological diagnosis of PEX were retrospectively identified (cases); from the same registry patients (controls) without rib cage abnormalities were randomly selected, until a 1:2 ratio was reached. The presence of pericardial effusion at CT was quantified. Follow-up was obtained for a composite end-point: cardiac tamponade, need for pericardiocentesis, need for cardiac surgery for relapsing pericardial effusion. Results: A total of 43 patients with PEX (20 females) and a control group of 86 cases (31 females) without rib cage abnormalities were identified. Pericardial effusion evaluated at CT was significatively more prevalent in patients with PEX vs control group, 37.2% vs 13.9% (p < 0.001), respectively; four patients with PEX (9.3%) had at least moderate pericardial effusion vs no subjects among the controls (p = 0.004). PEX diagnosis was significantly associated to pericardial effusion at multi-variate analysis (OR95%CI 10.91[3.47-34.29], p < 0.001). At a mean follow-up of 6.5 �� 3.4 years no pericardial events were recorded. Conclusion: Our findings support the higher prevalence of pericardial effusion in patients with PEX when compared to a control group. The absence of adverse pericardial events at follow-up suggest the good prognosis of these effusions, that in the appropriate clinical setting might not be considered "idiopathic".