In Deus Ex: Human Revolution, is it possible to get the pacifist achievement even if one kills enemies in the opening sequence? Boss fight kills do not count against the achievement, so I'm wondering if the same applies to the start of the game since you have fewer tools at your disposal.
According to this thread at Xbox360Achievements.org, kills in the opening sequence do count towards the achievement.
Since my original link died, the IGN Strategize on Deus Ex: Human Revolution also states that kills during the opening (pre-augmentation) sequence do count against the Pacifist achievement.
You can't kill, but you can shoot the yellow gas-canisters in the vicinity of enemies, that will render them unconscious.