Leontopithecus apparently is a seasonal breeder. In captivity in the Northern Hemisphere most litters are born from January to June. The estrous cycle averages about 2-3 weeks, and gestation averages 128 days, ranging from 125 to 132 days. Within a few days after a birth the father begins to carry the infant at times, and the father is the principal carrier after the third week of life. Life span in captivity, when the animals are well cared for, can be 15 years or longer.
Lion tamarins are among the world's most critically endangered mammals.
They are found in that part of Brazil with the densest human population. They have declined largely because of destruction of their forest habitat for lumber, agriculture, pasture, and housing. Until the 1960s they also were subject to considerable exportation for use in zoos, laboratories, and the pet trade. In the nineteenth century the species L. rosalia occurred across most of the present state of Rio de Janeiro. L. rosalia now is restricted to the Sao Joao Basin in Rio de Janeiro, where in 1973 its habitat totaled not more than 900 sq km.