Perilipins, members of the PAT protein family (named after lipid droplet proteins Perilipin, Adipophilin, and TIP47) are found exclusively at the surface of lipid droplets in adipocytes and steroidogenic cells. They have been suggested to function as regulators of lipolysis and triacylglycerol storage within adipose tissue. Four distinct isoforms ranging from perilipin A (57 kDa) to perilipin D (26 kDa) have been identified and they share an identical amino terminal sequences, and contain 2–6 consensus protein kinase A (PKA) phosphorylation sites. Perilipin C and D have been detected only in steroidogenic cells. Perilipin A is the most abundant form on the lipid droplets of adipocytes. The phosphorylation of perilipin by PKA, which is accompanied by the phosphorylation and translocation of hormone-sensitive lipase from the cytosol to the lipid droplets, promotes lipolysis. There is evidence for the presence of perilipin A in atheroma plaques suggesting that the protein may be involved in the development of therosclerosis by controlling as in adipocytes the hydrolysis of stored lipids.