During the “Our Planet Reviewed” French Guiana 2014-2015 expedition, Diptera were collected in seven habitat types over an approximately 1 km2 area in the Mitaraka Mountains of southwestern French Guiana. Sixteen collecting methods were used, seven of which yielded multiple samples containing Dolichopodidae. The survey produced a total of 4918 specimens of Dolichopodidae, belonging to 244 morphospecies, 31 genera including four new ones, and 10 recognized subfamilies. This is the highest dolichopodid species richness thus far recorded from a single location anywhere in the world. Three taxa could be identified to species level and all represent first records for French Guiana. Paraclius Loew, 1864, Chrysotus Meigen, 1824 and Medetera Fischer von Waldheim, 1819 were the most speciose genera. Paraclius represented by 50 species, exhibited an unprecedented species richness, mainly in the palm swamps. The three most productive methods in terms of numbers of specimens collected (68% of all specimens obtained using the three methods combined), SLAM traps, sweep nets, and a 6 m long Malaise trap, each yielded between 78 and 90 species, with approximately half of the species from each trap type unique to that method. Both blue, white or yellow pan traps, on the contrary, captured less than 20 species, and overall yellow traps were clearly the least efficient. Pan trap yields, however, were severely affected by repeated heavy rainfall. The highest species richness was recorded around the drop zone and in the base camp, on river banks and in river bank forests, with 40 to 60% of species unique to one of these habitat types. Forty-five species were collected on ‘savanes roches’, and 14 species on inselbergs, with four species shared by both types of rocky outcrops and uniquely found on them.