There are variables to take in consideration. At 100 HIding, technically you will hide 100 percent of the time if you are more than 7 tiles away from a hostile creature. Technically. Today my elf, with 125 dex Failed to hide with NO hostiles on screen at the Fan Dancer Dojo although I was being chased by a Ronin. My elf is GM HIding, and jeweled to 120 stealth/stealing. He failed repeatedly and subsequently died.
Skill, Dex, Race, Armor, and Range affect hiding and stealth. My thief with 125 dex is a much better stealther than my elven stealth mage with only 20 dex although the skills are the same. The thief never gets revealed. The mage does.