The southeastern Yucatan Peninsula hosts high numbers of transient Nearctic-Neotropic migrants during autumn migration, but the importance of this region during migratory stopover has not been addressed. We studied autumn stopover body mass gains among passerine migrants in tropical lowland forest 20 km inland from the Gulf of Honduras. Most individuals captured had some subcutaneous fat. Ten of 15 taxa with sufficient sample sizes had significant positive diel (24 hr) gains in a body condition index. Estimates of net mass gains in these 10 taxa suggested they all were depositing fat; average individuals in four of these taxa were depositing sufficient fuel to undertake an entire night of migration after only 1 day of fattening: Empidonax spp., Red-eyed Vireo (Vireo olivaceus), Gray Catbird (Dumetella carolinensis), and Northern Waterthrush (Seiurus noveboracensis). Two (Wood Thrush [Hylocichla mustelina] and Common Yellowthroat [Geothlypis trichas]) of the four species apparently not gaining mass at the study site migrate late in the season and occurred only after Hurricane Iris severely altered the habitat. Four other species (Gray Catbird, Magnolia Warbler [Dendroica magnolia], American Redstart [Setophaga ruticilla], and Indigo Bunting [Passerina cyanea]) had significant gains in mass after the hurricane. These data demonstrate the importance of the region as an autumn stopover site for some species and suggest that stopover areas farther north are also important to migrants passing through the southeastern part of the Yucatan Peninsula.