Parathesis costaricensis, P glendae, and P longipedicellata are described and illustrat- ed, and their phylogenetic relationships are dis- cussed. A key is provided to separate the new spe- cies. In addition, a new combination is made for Parathesis sinuata (from Colombia), and P ama- zonica Mez is lectotypified. The genus Parathesis J. D. Hooker contains 100 species distributed from northern Mexico to Pana- ma, the Caribbean, and throughout the Andes from Venezuela to Bolivia. The genus is defined by the unique glandular papillae of the calyx and corolla lobes, and bright yellow anthers. In preparation for our treatment of the genus Parathesis for Flora Me- soamericana, three new species from Costa Rica were discovered and are described herewith. A new combination from Colombia is also made, and Par- athesis amazonica is lectotypified.