SummaryMacleod’s or Swyer-Jamcs’syndrome (MLS) is characterized by abnormal hyperlucency of one lung or lobe, with the hyperlucent lung of normal size or smaller than the unaffected lung.Although most patients with MLS remain asymptomatic, they can sometimes present with a highly variable symptomatology. In this report we describe three patients with MLS of whom one presented no symptoms, the second an hemoptysis, and the third an unilateral pulmonary edema. These observations stress the important clinical heterogeneity of the Macleod’s syndrome.The diagnostic criteria of MLS arc reviewed, and a strategy to unravel the often difficult problem of unilateral lung hyperlucency is proposed.Acta Clin. Belg. 42, 4: 247–54.