NSO (Nurses Service Organization) is America’s largest provider of (nurse’s) malpractice insurance (the company currently has more than 500,000 policyholders throughout the country). NSO itself is a subsidiary of Aon Corporation. Although the company’s main focus is on professional liability coverage, it also offers standard forms of insurance. If you’re interested in purchasing an NSO policy click the “Quote” button on this page for a free online quote. Current policyholders can learn how to create an online account, make a payment, file a claim, and more on the “Login” page.