Income generation interventions, such as microfinance or vocational skills training, address structural factors associated with HIV risk. However, the effectiveness of these interventions on HIV-related outcomes in low- and middle-income countries has not been synthesized. We conducted a systematic review by searching electronic databases from 1990-2012, examining secondary references, and hand searching key journals. Peer-reviewed studies were included in the analysis if they evaluated income generation interventions in low- or middle-income countries and provided pre-post or multi-arm measures on behavioral, psychological, social, care or biological outcomes related to HIV prevention. Standardized forms were used to abstract study data in duplicate and study rigor was assessed. Of 5,218 unique citations identified, 12 studies met criteria for inclusion. Studies were geographically diverse, with 6 conducted in sub-Saharan Africa, 3 in South or Southeast Asia, and 3 in Latin America and the Caribbean. Target populations included adult women (N=6), female sex workers/bar workers (N=3), and youth/orphans (N=3). All studies targeted females except 2 among youth/orphans. Study rigor was moderate, with 2 group-randomized trials and 2 individual-randomized trials. All interventions except 3 included some form of microfinance. Only a minority of studies found significant intervention effects on condom use, number of sexual partners or other HIV-related behavioral outcomes; most studies showed no significant change, although some may have had inadequate statistical power. One trial showed a 55% reduction in intimate partner violence (adjusted risk ratio 0.45, 95% confidence interval 0.23-0.91). No studies measured incidence/prevalence of HIV or sexually transmitted infections among intervention recipients. The evidence that income generation interventions influence HIV-related behaviors and outcomes is inconclusive. However, these interventions may have important effects on outcomes beyond HIV prevention. Further studies examining not only HIV-related outcomes, but also causal pathways and intermediate variables, are needed. Additional studies among men are also needed.