Metastatic infiltration is most frequent than primary pericardiac tumors. Most frequent tumors are adenocarcinoma and lymphomas. A retrospective analysis of 18 oncological patients with significant pericardiac effusion (SPE) is carried out. The conclusions of the study are: SPE can be the first manifestation of a neoplasm; frequently, pericardiac tamponade (PT) has a neoplastic origin; thorax is the most frequent localization of the primary tumor; pericardiac fluid (PF) cytology analysis has low diagnostic yield; most useful diagnostic tests are thoracocentesis, thorax computerized tomography (CT) and bronchoscopy; SPE in a neoplasm suggest poor short-term prognosis; poor prognosis variables in this series were primary tumor unfavorable histology, advanced tumor disease and (probably) presentation as PT.