Most monsters and NPC roll individual rolls for each of their HD to get their points, rather than taking the average.

Player characters, henchmen (and special NPC leaders, if you like) Begin with maximum hit points for first level, and roll 2 HD each level thereafter, taking the better of the 2. So when a player creates a Fighter named Rocko the Invincible he will get 8 hp for first level. At second level, he rolls a 1 on the first and a 7 on the other, adding 7 to his Hp total..