The outbreak in Konlang village in Pakbeng district of Oudomsay province (No.7) was initially investigated by health workers at the dispensary and diagnosed as measles, but we found clinical features of the cases on the skin showing the typical manifestations of chickenpox; from macule to papule to vesicle to scabs, and all IgM antibodies of five samples were negative. The gene discussed is CD40LG; the disease is chickenpox.