ObjectiveThis study aims to determine the distribution of blood groups and the demographic background of blood donors in a referral hospital in Northern Tanzania.ResultsThe most common blood group was O (52.3%) and the least common was AB (3.18%). 97.7% of the blood donors were Rh positive and the rest were Rh negative. Most donors were young adults, representing the age group of 19–29. The majority of donors were male (88.1%) and the majority (90.8%) were replacement while the remainder was voluntary donors.