Three new species of Pleurothallidinae (Orchidaceae) from Costa Rica, Acianthera fecunda, A. hamata, and A. cabiriae, are described and illustrated. Acianthera hamata is closely related to A. cogniauxiana, from which it differs mainly in the shape of the leaves; the hooked rachis of the inflorescence; the smaller flower size; the entire petals, provided with a rounded lobe on the lower side; and the broadly flabellate keels of the lip. Acianthera fecunda is distinguished by its cleistogamous flowers, reduced habit size, and 2-flowered, short inflorescence. Acianthera cabiriae is closely related to A. fecunda, from which it differs in plant size, the elliptic leaves, and the 3- to 4-flowered inflorescences.