Objective: During the last 2 decades, right/left hemisphere dominance was supposed to affect the immune system differently. Experimental and clinical observations indicate that the left hemisphere plays a crucial role in the development of the immune system. The true relationship between immune response and acute ischemic stroke laterality remains to be elucidated. Methods: We studied acute right-handed stroke patients admitted to a single acute neurology department with a specialized stroke unit. Being part of our clinical protocol, blood samples were taken within the first 24 h after the onset of stroke symptoms. The medical record of each patient was reviewed, and demographic, clinical laboratory (key criteria: C-reactive protein, CRP, and white blood cell count, WBC) and neuroimaging information was retrieved. All data were presented descriptively, and bivariate test statistics, ANOVA (log-transformed data) or linear correlations were calculated. Results: Fifty-six of the 187 patients admitted to our Stroke Unit between October 2003 and March 2004 with different stroke subtypes according to the TOAST criteria were retrospectively evaluated in order to characterize the impact of stroke laterality on immunoregulatory response measured by CRP levels and WBC. Correlation analysis revealed that left-sided ischemic stroke yielded a significantly higher correlation between CRP levels and WBC. Following left-sided stroke, a more marked variability in CRP and WBC was found compared to patients with right-sided ischemic stroke, although ANOVA did not show significant differences between immune response values as a function of stroke subtypes. Conclusions:We identified an association between stroke laterality and immunoregulatory response in patients with acute ischemic stroke. Left-sided stroke may be considered as a direct risk factor for infectious disease or immune deficits and should attract special attention. However, these preliminary results need be confirmed by controlled studies. Copyright (c) 2006 S. Karger AG, Basel.