Most common type (90%).
Radiolucent (10% opaque due to calcium)
Risk factors - fat, fertile, 40. Age (40s), estrogen (oral contraceptives, mult. preg., females, obesity) (^ HMGco-A reductase-> ^ chol. synth AND ^ lipoprotein receptors on hepatocytes, ^ uptake of chol by liver), clofibrate (lipid lowering agent- ^ HMG co-A reductase activity, dec. conversion of chol to bile acids), Native american ethnicity, crohn disease (dec. uptake of bile salts and acids), & cirrhosis (dec. prod. of bile salts).