Cryptosporidiosis is an important disease in calves and in immune-compromised persons especially people living with HIV/ AIDS. Cryptosporidium parvum is the most important zoonotic pathogen transmitted from calves to human beings but other zoonotic Cryptosporidium Spp. like C. meleagridis, C. felis, C. canis, can also be found to be opportunistic infection in HIV/AIDS patients. The epidemiology of Cryptosporidiosis in humans is not completely understood due to the existence of multiple transmission routes which made prevention and control difficult. This study was carried out in Hawassa, Southern part of Ethiopia to determine the prevalence of cryptosporidiosis in HIV/AIDS patients and in diarrheic calves. The potential risk factors associated with human Cryptosporidiosis in identified positive cases were assessed, with emphasis on the role of diarrheic calves in the transmission of the disease.