BACKGROUND INFORMATION Mother-to-Child-Transmission (MTCT) is a major public health problem in Sub-Saharan Africa (SSA) affecting the lives and livelihood of many. Of the 33 million people infected globally with HIV, over 22 million are living in SSA and 12 million of them are women of reproductive age. A combination of high fertility levels and the high number of women infected with HIV results in high rates of MTCT. Paediatric HIV has been shown to increase levels of infant and child mortality by 2-3 folds in worst affected counties and have contributed to 9% of all maternal deaths in SSA. Most efforts to prevent MTCT of HIV have focused mostly on the third prong of the Preventing Mother-to-Child-Transmission (PMTCT) a strategy which offers Anti-Retroviral Therapy (ART) drugs to HIV infected pregnant women and their exposed infant. This method is complex, labour intensive and has very low Mother and Infant follow-up rates after delivery. However, the effective use of contraceptives as suggested in the second prong of the PMTCT strategies has the ability to reduce the rates of MTCT at a similar or even lower cost compared to the third prong. It also has the potential to reduce the rate of maternal deaths. There is limited information on the levels of contraceptive use among HIV-positive women and the associated factors in general SSA including Tanzania. AIM The aim of this study is to determine the prevalence of modern contraceptive use and its associative factors among HIV-positive women aged 15 – 49 in Arusha City, Tanzania. METHODOLOGY The study was a cross-sectional study conducted during April – May 2011. Questionnaires were used to collect necessary information during face-to-face interviews among women attending Care and Treatment Centres in Arusha Municipality during the study period. A checklist was used to gather information on contraceptive availability at selected health facilities. Data was entered and analysed using SPSS. Descriptive and inferential statistics were used to summarize the data. RESULTS In total, 309 women participated in the study. Their ages ranged from 15- 49 with a mean age of 33. The prevalence of modern contraceptive use among HIV infected women was 72%. The most common methods of modern contraceptives used were male condoms, Depo-Provera and Oral Contraceptive Pills (OCP). Prevalence of dual contraceptive use was 29%. Independent predictors of modern contraceptive use were participants’ plan to have more children, children having the same father, sexual activity, ever been counselled on dual contraceptives, and awareness on contraceptives. CONCLUSIONS AND RECOMMENDATIONS This study prevalence of contraceptive use among HIV-positive women was high in Arusha city. However, further studies need to be done to corroborate the findings including a larger sample and stratifying the women according to ART use. The study also found that the most commonly used type of modern contraceptives were condoms. While the use of condoms is good in preventing transmission of HIV the adequate use of modern contraceptives used to prevent unintended pregnancies were lacking and need to be further explored and promoted, particularly in view of the complexities and broader consequences of MTCT. Health planners need to come up with counselling messages that aim to improve use of effective pregnancy prevention methods as well as strategies to improve contraceptive use among 30% of non-users.