They are related to guinea pigs and look quite similar, but have longer legs. The species vary in color from tawny to dark brown with lighter underparts. Their bodies are covered with coarse hair which is raised when alarmed. They are about 20 inches (51 cm) in length, with short, hairless tails. Agoutis have five front and three hind toes; the first toe is very small. The tail is very short or nonexistent and hairless. The molar teeth have cylindrical crowns, with several islands and a single lateral fold of enamel. Agoutis may grow to be up to 60 centimetres (24 in) in length and 4 kilograms (8.8 lb) in weight. Most species are brown on the back and whitish or buffy on the belly; the fur may have a glossy appearance and then glimmers in an orange colour. Reports differ as to whether they are diurnal or nocturnal animals.
Agoutis are found in forested and wooded areas in Middle and South America. Their habitats include rainforests, savannas and, nowadays, cultivated fields, depending on the species. They conceal themselves at night in hollow tree trunks or in burrows among roots. Active and graceful in their movements, their pace is either a kind of trot or a series of springs following one another so rapidly as to look like a gallop. They take readily to water, in which they swim well.