OBJECTIVEThis article evaluates the use of modern contraceptives among poor women exposed to a family planning voucher program in Cambodia, with a particular focus on the uptake of long-acting reversible contraceptives (LARCs).METHODSWe used a quasi-experimental study design and data from before-and-after intervention cross-sectional household surveys (conducted in 2011 and 2013) in 9 voucher program districts in Kampong Thom, Kampot, and Prey Veng provinces, as well as 9 comparison districts in neighboring provinces, to evaluate changes in use of modern contraceptives and particularly LARCs in the 12 months preceding each survey. Survey participants in the analytical sample were currently married, non-pregnant women ages 18 to 45 years (N = 1,936 at baseline; N = 1,986 at endline). Difference-in-differences (DID) analyses were used to examine the impact of the family planning voucher.RESULTSModern contraceptive use increased in both intervention and control areas between baseline and endline: in intervention areas, from 22.4% to 31.6%, and in control areas, from 25.2% to 31.0%. LARC use also increased significantly between baseline and endline in both intervention (from 1.4% to 6.7%) and control (from 1.9% to 3.5%) areas, but the increase in LARC use was 3.7 percentage points greater in the intervention area than in the control area (P = .002), suggesting a positive and significant association of the voucher program with LARC use. The greatest increases occurred among the poorest and least educated women.CONCLUSIONA family planning voucher program can increase access to and use of more effective long-acting methods among the poor by reducing financial and information barriers.