You've got to give us a lot more information than that.
Some prestige classes are balanced better for some games than for others. Some are too weak or too powerful regardless of the campaign.
As a general rule of thumb, a prestige class should not be inherently more powerful than a base class when compared side-by-side - only different. The more outlandish or powerful the advantage gained, the more narrow-focused or limited the prestige class should be in other areas.
Let me give you an example of a broken prestige class: The Radiant Servant of Pelor from Dragon Magazine. Compared to a Cleric of the same level, the Radiant Servant gains Radiance (double the radius of all spells with the "light" descriptor), Extra Greater Turning (3+ Cha modifier), Martial Weapon Proficiency, a third domain, Aura of Warding (+2 Will saves for all within 10 feet), Positive Energy Burst (d8 per prestige class level damage verses undead), Empower all healing spells, Maximize all healing spells, and +1 caster level every level to boot. In contrast, the Radiant Servant loses an average of 10 hit points over the lifetime of the character (d6 HD, down from the cleric's d8).
Broken. In our campaign, my DM got rid of Aura of Warding and the Martial Weapon proficiency. I suggested he also remove a couple spell levels, but he declined.
That's just one example. You've got to be careful with prestige classes. Yeah, they are cool, and yeah, they make great ways to create a unique feel for your world, but they should never be more powerful than a base class. Just different.