HIV is a world wide health problem that most adversely affects people in developing countries with low income and little health education. Most children living with HIV aquire the disease from their HIV-positive mothers during pregnancy, delivery and breastfeeding. Antiviral prophylactic treatment has been well established during pregnancy and delivery. In developed countries HIV-positive mothers are adviced to formula feed their infants, while in developing countries this poses a greater risk for the child to die because of other factors, such as malnutrition, diarrhea and pneumonia. Antiretroviral treatment during pregnancy and breastfeeding are some of the biggest issues of todays prevention-of-mother-to-child-transmission (PMTCT) research. Reducing the risk of transmission of HIV through breast milk to a minimal will be important for the overall transmission of the virus to children of HIV-positive mothers. A threat to the HIV-prophylactic treatment is the development of resistence to the medication being used. Hopefully, the awereness of the problem will prepare health workers to establish regimens that will reduce this risk. Haydom Lutheran Hospital in the Mbulu district in Tanzania is a hospital that focuses on HIV and PMTCT, with a special interest in prophylactic treatment of HIV-positive mothers while breastfeeding. During the summer of 2007 we spent four weeks at the hospital, observing the PMTCT work at the HIV center, including mobile health clinics. This thesis is about HIV transmition from mother to child, WHO guidelines, and guidelines for, and an observation of, the PMTCT work at Haydom Lutheran Hospital.