The tropical forests of the Chocó region support one of the largest concentrations of plant species in the world. Palms (Arecaceae) are one of the most important families in the Chocó lowlands, but their ecology remains little studied. We studied the diversity of palm communities in the Chocó and the relationship between diversity and precipitation in 48 transects distributed along a precipitation gradient covering 2000–10 000 mm annual rainfall. In each transect (5×500 m) all species of palms were identified, and all individuals were counted. We recorded a total of 57 species of palms (mean ± SD: 17 ± 8 in each transect) and we counted 37 955 individuals (791 ± 446 per transect). We found that palm richness and abundance were significantly related to precipitation (r2 = 0.86; P > 0.001). We also found that palm community composition was strongly correlated to the geographic distance between transects (rm = 0.63; P = 0.001). The recorded palm richness is one of the highest for the Neotropics. In addition, it is the first time that this relationship between precipitation, richness, and abundance of palms is documented at the regional level for the Chocó biodiversity hotspot.