The El Toro Wilderness, designated by Congress in 2005, occupies about 36 percent of the 11,300 ha Luquillo Experimental Forest (LEF) in northeastern Puerto Rico. It is the only tropical forest in the wilderness system managed by the U.S. Department of Agriculture. El Toro extends from 370 to 1,074 m in elevation, and is occupied by four forest types found in the mountainous Caribbean: lower montane rain forest, montane rain forest, palm brake, and dwarf forest. The LEF, a Biosphere Reserve since 1976, contains 225 tree species, 45 of them endemic to Puerto Rico, and 23 to the LEF alone; 150 species of ferns; 79 species of orchids; 11 native bats; 101 birds, 12 of them endemic to the island; 19 native reptiles, 8 endemic; 14 native amphibians, 8 endemic; and 6 native fish species. Most of these species occupy the wilderness. The LEF's century of research has provided a wealth of useful information on local climate, geology, soils, water resources, flora, fauna, and ecology. Temporary and permanent plots established within the wilderness have provided information on forest structure and species composition along elevation and topographic gradients. El Toro, surrounded by a dense human population, is under multipurpose management. Future research should demarcate wilderness boundaries and wildlife habitat requirements, and monitor for environmental changes. El Toro must be managed for solitude, an uncommon resource on an island where stakeholder support for wilderness is lacking.