Four patients underwent cataract extraction with implantation of intraocular lenses. Preoperative ultrasonography did not include a comprehensive diagnostic B-scan analysis. Postoperative examination revealed uveal melanomas. The clinical presentations as well as the histopathologic findings of the two enucleated eyes are discussed. These cases emphasize the necessity for B-scan ultrasonography prior to cataract surgery when media opacity prevents adequate visualization of the fundus.