An important parasitic infection among HIV infected patients is the cryptosporidiosis. Cryptosporidium parvum is an intestinal parasitic protozoon that causes severe diarrhea and may lead to death in immunocompromised hosts. In HIV infected cases with cryptosporidiasis, four main clinical syndromes were identified: chronic diarrhea, choleralike disease, transient diarrhea, and relapsing illness. In this paper, the authors presented the prevalence of cryptosporidiosis among Thai HIV-infected patients with diarrhea in comparison to the previous noted prevalence in the past decade. The prevalence of among Thai HIV infected patients with diarrhea in the previous decade is equal to 7.14 %. The present prevalence of among Thai HIV infected patients with diarrhea is investigated with the same protocol. Overall 25 HIV infected cases could be detected giving the prevalence equal to 18.95 % (25/193). Of interest, although the HAART therapy is easily available in Thailand, at present the prevalence of cryptosporidiosis is still very high in the HIV seropositive patients with diarrhea. Therefore, the authors hereby propose that the wide distribution of HAART therapy did not affect the prevalence of cyrptosporidiosis among HIV seropositive patients with diarrhea.