With the recent changes to Facebook's privacy settings came the decision to open up a user's friends list to anyone who visited their profile. After a hue and cry from Facebook users and advocacy groups, Facebook relented and provided a way to hide the friends list. Unfortunately, they didn't make it altogether easy to find out how to hide your Facebook friends list.
Don't bother looking in the privacy settings. For some reason, Facebook decided to bury the setting in the profile itself.
To hide your Facebook friends list, go to your profile page and locate the Friends box in the left column. There is a small icon of a pencil in the upper right-hand corner of the friends box that will open a small window containing the settings. Simply uncheck the box marked "Show my friends on my profile" and your friends list will no longer show up to visitors.