Innovative combination HIV-prevention and microfinance interventions are needed to address the high incidence of HIV and other STIs among women who use drugs. Project Nova is a cluster-randomized, controlled trial for drug-using female sex workers in two cities in Kazakhstan. The intervention was adapted from prior interventions for women at high risk for HIV and tailored to meet the needs of female sex workers who use injection or noninjection drugs. We describe the development and implementation of the Nova intervention and detail its components: HIV-risk reduction, financial-literacy training, vocational training, and a matched-savings program. We discuss session-attendance rates, barriers to engagement, challenges that arose during the sessions, and the solutions implemented. Our findings show that it is feasible to implement a combination HIV-prevention and microfinance intervention with highly vulnerable women such as these, and to address implementation challenges successfully.