You are skilled at avoiding detection, allowing you to slip past foes or strike from an unseen position. This skill covers hiding and moving silently.
Your Stealth check is opposed by the Perception check of anyone who might notice you. Creatures that fail to beat your Stealth check are not aware of you and treat you as if you had total concealment. You can move up to half your normal speed and use Stealth at no penalty. When moving at a speed greater than half but less than your normal speed, you take a –5 penalty. It's impossible to use Stealth while attacking, running, or charging.
Breaking Stealth When you start your turn using Stealth, you can leave cover or concealment and remain unobserved as long as you succeed at a Stealth check and end your turn in cover or concealment. Your Stealth immediately ends after you make an attack roll, whether or not the attack is successful (except when sniping as noted below).
Source: Giant Hunter's Handbook
Large bodies that break your opponent's line of sight can sometimes be just as useful as darkness for hiding your position.
Special: Normally the soft cover provided by other creatures is not sufficient to allow you to attempt a Stealth check. Soft cover provided by creatures at least one size category larger than you does allow you to attempt Stealth checks against other creatures not already aware of your presence at a –10 penalty. If the creature providing the cover knows which square you occupy and is trying to avoid concealing you, this penalty increases to –20.
You can also hide from a creature by staying under its own body if it is at least two size categories larger than you and you are in its space. Such attempts also take a –10 penalty, which increases to a –20 penalty if the creature is aware you are in the area. If the creature moves away from you, you are automatically revealed, unless you have readied an action to move with it.
If you've already successfully used Stealth at least 10 feet from your target, you can make one ranged attack and then immediately use Stealth again. You take a –20 penalty on your Stealth check to maintain your obscured location.
Usually none. Normally, you make a Stealth check as part of movement, so it doesn't take a separate action. However, using Stealth immediately after a ranged attack (see Sniping, above) is a move action.