What are gallstones? Gallstones, or cholelithiasis, form when substances in bile, primarily cholesterol or unconjugated bilirubin, crystallize within the gallbladder. Find our full video library only on Osmosis: http://osms.it/more. Join millions of current and future clinicians who learn by Osmosis, along with hundreds of universities around the world who partner with Osmosis from Elsevier to