Background Limited data are available on characteristics of viral encephalitis in patients after allogeneic stem cell transplantation.Design and Methods We analyzed 2,628 patients after allogeneic stem cell transplantation to identify risk factors and characteristics of viral encephalitis.Results Viral encephalitis occurred in 32 patients (1.2%, 95% confidence interval 0.8%–1.6%) and was associated with the use of OKT-3 or alemtuzumab for T-cell depletion (P