Monstera alfaroi Croat & M. Cedeño, M. tarrazuensis Croat & M. Cedeño and M. wilsoniensis M. Cedeño & Grayum, all apparently endemic to central and southern Costa Rica at middle elevations on the Pacific slope, are described as new species. Monstera alfaroi is characterized by having warty light brown petioles with undulate sheaths, very large adult leaves and inflorescences with warty peduncles, and externally light green spathes. Monstera tarrazuensis is characterized by its smooth, light green petioles with white dots and deciduous sheaths, coriaceous, entire leaf blades and inflorescences on hanging stems. Monstera wilsoniensis is characterized by its deciduous petiole sheaths, cordate or subcordate, weakly or not fenestrated leaf blades with entire margins and numerous primary lateral veins, and inflorescences in ascending or hanging stems. The three novelties are compared, respectively, with M. buseyi Croat & Grayum, M. luteynii Madison and M. adansonii Schott, and all are illustrated with color photos of living material.