Dissertation (MSc Mental Health Nursing)Background: Globally around 13million people are injecting drugs and 1.7million of them are living with HIV. Injecting drug users have created and remain a major international public health problem. Objective: This study aimed to determine factors associated with high risk of injection behaviors among injection drug user (IDU’s) in Zanzibar. Methods: A cross-sectional study design using a quantitative approach was conducted in Zanzibar islands. A total of 1308 injection drug users aged 15 to 64 years were interviewed on this study. A face to face interview through self-administered: questionnaires were and were selected from the four districts out of 11and 20shehia out of145.Mental hospital, methadone clinic, hot spot, lower spot, sober rehabilitation house. Results: A total of1308 respondents participated in this study on which 660 (50.5%) engaged on high risk injection behaviors. Low-risk behavior 648(49.5%). Where by the minority were females 293(22.4%) while the majority ware males about 1017(77.7%). Based on the multivariate logistic regression analysis, participants aged above 24 years were found to have a high risk of injection behaviors (AOR 2.287 95%CI 1.298 – 4.030 P < 0.05), compared to those aging between 18 to 19 years. Those who lived in lower spot areas had 1.728 odds of engaging on high risk behaviors compared to those living in hot spot areas (95% CI 1.188 – 2.513 P< 0.05), also females participants were found to have low risk of engaging on high risk injection behaviors (AOR 0.628 95%CI 0.431 – 0.915 P < 0.05) than males. Conclusion: This study,high-risk injection behaviours was very prevalent among (IDUs)including sharing insruments, needles, and swabs when injecting drugs. Majority were found to be engaged on high risk injection behaviours. Male were moreengaged on high-risk injections. For those whom had lived on hot spot areas were most engaged on high risk injection behaviors. long duration of drugs for long time 11 or more than 11 years