Relationships between soil erosion on hillside farms and forest conversion to farmland in adjacent national parks were examined in the Bayhang watershed near Leyte Mountains National Park, Philippines, and the Sungai Ning watershed near Kerinci-Seblat National Park, Indonesia. A random sample of hillside farms revealed widespread evidence of accelerated soil erosion in both watersheds, including splash and sheet erosion, and rill and gully formation. Erosion under line transects and on enclosed runoff plots revealed mean soil losses of 422 t/ha during the first six months of cultivation on recently cleared farms in Bayhang and 3.8 t/ha during the cropping year on continuously cultivated farms in Sungai Ning. Analysis of eroded sediments and uneroded soils revealed erosion-induced reductions in soil productivity. Soil erosion and land degradation were found to contribute to forest conversion in both national parks. The farmers' response to land degradation in Bayhang was to clear forest for new farms in Leyte Mountains National Park, while farmers in Kerinci replaced nutrient-demanding crops with cassava, and cleared forest for new farms in Kerinci-Seblat National Park. Potentially sustainable and appropriate soil conservation and economic development activities for use in the two watersheds are reviewed.