Here we have studied some biochemical and molecular characteristics of lipid metabolism in the Hydra cnidarian polyp. We have characterized variations in lipid metabolism in response to diet by establishing lipid profiles in starved and fed Hydra, and quantifying with the Red Nile technique the accumulation of lipid droplets in the digestive cells upon starvation. As expected, Hydra uses lipid reserves as fuel for survival, suggesting that fatty acids and cholesterol in the diet are esterified and stored when abundant and then released when fasting. During regeneration, specific classes of lipids appear to be needed, possibly for cell membrane synthesis and/or specific signalling. We finally identified five orthologs of the bilaterian genes encoding the dihydrolipoamide branched-chain transacylase (DBT), hydroxyacyl-CoA dehydrogenase (HCD), choline phosphotransefrase (CHPT), phosphatidylcholine Sterol-O acyltransferase (PCSAT) and lipophorin receptor /LDL (LpR/LDL). Phylogenetic analyses confirm that these enzymes and receptor essential for lipid metabolism are conserved in eumtazoans.