This paper aims at making a critical examination on criminalisation of intentional transmission of HIV/AIDS where the main focus is on evidential challenges under the laws of Tanzania that render the criminalisation practically unrealistic. The challenges lie on how to prove intentional transmission of HIV/AIDS beyond reasonable doubt which is a required standard in all criminal cases. The paper reveals that HIV is scientifically proved not to be something specific and unique to every individual as it is the case with the DNA or fingerprints. Thus, it has been established that in Tanzania, it is almost impossible to prove beyond reasonable doubt that one person intentionally transmitted HIV/AIDS to another. Eventually, the author recommends that if the policy and lawmakers are concerned about preventing HIV transmission through penal laws, it is better to address the evidential challenges surrounding this matter first so as not to deal with the HIV problem to the expense of those who are already its victims. Key Words: HIV/AIDS, Criminalisation, Intentional Transmission.