Summary The decomposition of cholesterol 20α- and 25-hydroperoxides was studied by gas chromatography. Cholesterol 20α-hydroperoxide decomposed to 3β-hydroxypregn-5-en-20-one, androst-5-en-3β-ol, cholest-5-ene-3β, 20α-diol, androst-5-ene-3β, 17β-diol, and androsta-5,16-dien-3β-ol. Cholesterol 25-hydroperoxide decomposed to cholest-5-ene-3β, 25-diol, chol-5-en-3β-ol, pregn-5-en-3β-ol, and 3β-hydroxy-27-norcholest-5-en-25-one. These thermal decomposition patterns, similar to but different from that of autoxidation products in air-aged cholesterol, account suitably for the presence of degraded steroids in air-aged cholesterol. Analogies are drawn between the autoxidation of cholesterol via hydroperoxide intermediates with subsequent spontaneous decomposition and the biological oxidation of cholesterol to give similar types of products.