Twenty-two new species of Zadbimyia, a new genus of the tribe Asynaptini, are described from Costa Rica, the first new descriptions of Neotropical Porricondylinae (Cecidomyiidae) in modern times. The new species are: Zadbimyia aberrans, Z. anniae, Z. artborkenti, Z. browni, Z. carolinae, Z. costaricensis, Z. dubia, Z. elenae, Z. elviae, Z. holdenae, Z. inornata, Z. lasalturas, Z. marcoi, Z. membranacea, Z. minima, Z. spinapiscis, Z. talamanca, Z. tapanti, Z. viquezi, Z. wendyae, Z. zumbadoi, and Z. zurqui. All species were found during the Zurquí All-Diptera Biodiversity Inventory, in mid-elevation (1600 m) cloud forest in the central highlands of Costa Rica. A maximum of 19 species occurred at a single site. Pseudocamptomyia Parnell, a genus known from one species in northeastern United States and possibly two species in Somalia, was identified as the closest relative of Zadbimyia. Ultraviolet light traps proved to be the most effective device to collect adults of Zadbimyia. As a peculiarity in Porricondylinae, the circumfila of Zadbimyia males are multi-looped and not substantively different from the circumfila known from male Cecidomyiidi (subfamily Cecidomyiinae).