Haemophagocytic syndrome (HS), also referred to as haemophagocytic lymphohistiocytosis or macrophage activation syndrome, comprises a heterogeneous group of disorders featuring sepsislike characteristics typically combined with haemophagocytosis, hyperferritinemia, hypercytokinemia and variable cytopenias, often resulting in fatal multiple organ failure. The availability of widely accepted diagnostic and therapeutic guidelines for the hereditary, paediatric forms of HS has improved outcome and lead to a better pathophysiological understanding. Although similar, reactive (secondary) HS in adults are distinct from childhood forms. Limited awareness of this type of disorder and the absence of clinical guidelines are to blame for delayed diagnosis and dire prognosis in many cases of HS in adults. Moreover, the underlying mechanisms of adult HS remain to be unravelled yet. We summarise general features of HS and discuss particular characteristics of this disorder inadults. Furthermore, we describe a simple screening and diagnostic algorithm based on serum markers of macrophage activation (ferritin, soluble CD163 and soluble CD25) and morphological evidence of haemophagocytosis. Application of this strategy might be instrumental for recruiting patients for clinical studies, early diagnosis and hence improved prognosis. Indeed, there is evidence that a subgroup of patients with systemic inflammatory response syndrome presenting with signs of macrophage activation benefit from early administration of intravenous immunoglobulins. Clinical studies are needed to validate our diagnostic approach and to establish well defined prognostic and therapeutic algorithms. Finally, we will discuss whether similar processes contribute to HS in adults compared to childhood forms.