[Unilateral alveolar effusions (author's transl)]

The unilateral alveolar effusions can be divided into two groups: those which take place in an already diseased lung (ipsilateral), and those which take place in the healthy one (contralateral). Starting from the most recent literature, the causes of the two different radiological features are discussed. Some cases of alveolar effusions, both ipsilateral and contralateral, are reported.