Protozoa of the genus Cryptosporidium are small coccidian parasite known to infect the mucosal epithelium of a variety of animals including human, causing fatal course in immunodeficient patients as well as self-limited illness in healthy individuals. Various life cycle stages including trophozoite, meront, merozoite, gametocyte and oocyst in infected mucosa are a diagnostic feature. Electron microscopy (EM) provides sufficient findings for genus and species identification of this parasitic organism. The authors presented scanning and transmission EM findings of Cryptosporidium parvum infection in two children: one with acute lymphoblastic leukemia and the other without any evidence of immune compromise.