Timor-Leste is a small, poor and predominantly-agricultural nation of less than 1 million people. Most families suffer from chronic food insecurity practising food rationing 1–6 months of the year. The small size of Timor-Leste, its recent birth as a nation and conflict history, together with little previous research on staple crops make it a unique crucible to test the effect of a major post-conflict initiative of agriculture research on national food security. Research started in 2000 with the introduction of germplasm of staple crops (maize, peanut, rice, cassava and sweet potato). Replicated trials confirmed by extensive evaluation in farmer-managed trials revealed significant yield advantages over the local cultivar in maize of 53%, in peanut of 31%, in rice of 23% and in sweet potato of 80%, accompanied by improvements in size and eating quality. Cultivars of maize (2), peanut (1), rice (1) and sweet potato (3) were released in 2007. One year later an early adoption study of 544 farmers involved in on-farm trials showed that 73% had re-grown new cultivars. Cultivar adoption not only increased household food security but often produced surpluses for sale in the market—sometimes for the first time. The project is planning to increase seed production and dissemination to move from a highly positive pilot-scale impact in six Districts to impact food security nationally.