1. Inflammation and activated leucocytes are involved in the pathogenesis of acute ischaemic stroke. Leucocyte apoptosis is critical for the efficient resolution of inflammation. Little is known about the correlation between leucocyte apoptosis and acute ischaemic stroke (AIS). The objective of the present study was to evaluate the role of leucocyte apoptosis in patients with AIS. 2. Serial changes in leucocyte apoptosis and the apoptosis of leucocyte subsets (i.e. neutrophils, monocytes and lymphocytes), as determined by flow cytometry, were examined prospectively at various time-points in 50 patients with AIS and 50 controls using the APO 2.7 antibody. 3. Leucocyte apoptosis and the apoptosis of leucocyte subsets were significantly lower in stroke patients than in the control group (P < 0.01). The percentage apoptosis of total leucocytes and neutrophils was significantly lower in the group with large-artery disease than in the group with small-atery disease (P < 0.01). Leucocyte apoptosis was lowest during the acute stage of ischaemic stroke and increased thereafter. 4. Leucocyte apoptosis may reflect the inflammatory status after AIS. A better understanding of the mechanisms underlying leucocyte apoptosis in ischaemic stroke may lead to the development of new strategies to improve the outcome for stroke patients.