IntroductionBlood is an important requirement in different medical and surgical conditions with half of all donations are from developing countries. Lack of eligibility among blood donors who present for blood transfusion, called blood donor deferral is associated with the unsustainable and inadequate amount of blood collected by blood banks worldwide. However, the prevalence and causes of blood donor deferrals are not well known in Tanzania where less than one-third of actual needs of blood is collected, leading to unmet demand of blood for transfusion, and causing unwanted morbidity and mortality.Materials and methodsThis was a retrospective analysis of blood donors at northern zone blood transfusion center, Tanzania from January to December. 2016. Donor’s data were transferred to Statistical Package for Social Studies (SPSS) program version 20.0 for analysis. Descriptive statistics was used to summarize data and comparisons made by type of donor and deferrals using Chi-square test.ResultsA total of 14377 participants were studied whereby 12775 (88.9%) were voluntary non-remunerated blood donors. The blood donor deferral rate was 12.7% and deferral was significantly more likely in females, with increasing age above 31 years, who came from nearby regions from where the blood bank is located and/or a family replacement donor (P value <0.01). Overall, infections contributed to 62% of all deferrals and low hemoglobin was the leading cause of temporary deferrals while Hepatitis B lead the permanent deferral causes.ConclusionsBlood donor deferral is a significant problem in northern Tanzania and accounts for more than one-tenth of all prospective blood donors. Latent and active infections are the leading cause of blood donor deferrals, a picture that mirrors other low income countries especially those located in sub-Saharan Africa. Results of this study calls for appropriate preventive interventions to address prevalent causes of deferrals such as infections with HIV and HBV to tackle low hemoglobin.