The assessment of risk comes almost second-nature to insurance professionals. But according to a recent survey by Towers Watson, there are still extreme risks that can keep insurance executive awake at night. As part of the professional services companys regular biennial analysis of the extreme risks likely to affect the broader investment community, Towers Watson polled insurance executives to categorize the rare events that would have a significant impact on global economic growth and asset returns if they occurred. More than 30,000 votes were compiled in a wiki survey, which enabled participants to add their own ideas. What follows are the top 10 extreme risks as identified by the respondents.