This paper provides a revision of the foliicolous representatives of the Gyalectaceae in Costa Rica. Five species of Coenogonium and 13 of Dimerella are distinguished. Coenogonium interplexum, C. interpositum, C. leprieurii, C. linkii and Dimerella vezdana are ubiquitous as to the choice of their substratum, whereas C. moniliforme and Dimerella lutea are facultatively foliicolous. The remainder are typically foliicolous taxa but may occasionally be found on bark. The following species are for the first time reported as foliicolous from Costa Rica: Coenogonium interplexum, C. interpositum, C. leprieurii, C. moniliforme, Dimerella fallaciosa, D lisowskii, and D. aff. pilifera. Three new species are described: Dimerella isidiifera sp. nov. with disciform isidia, D. subzonatasp. nov. with small, bright yellow, dentate apothecia and a whitish prothallus, and D. siquirrensis sp. nov. with large, orange apothecia and a thin whitish prothallus. A key is presented for neotropical foliicolous Gyalectaceae, and notes on the distribution and ecology of the species are given.