Special bonuses are the extra points given after each operation based on skill during the operation. The requirements to obtain these bonuses are much more lenient in easier modes, but require more skill at higher difficulties. This score is added to the operation score, vital bonus, and time bonus to get the final operation score. Scoring all the bonuses is usually key to getting the S or XS rank in many operations.

In Under the Knife, the Special Bonuses are not listed, but instead merely contribute to a general "Special Bonus" when the score is being totalled. In Second Opinion and Under the Knife 2, these bonuses give fixed scores, while in New Blood they give multipliers to the "Skill Score", which in turn comprises of the Vitals, Time, and Chain Length Bonuses.

Common bonus criteria are:

  • Completed with X seconds left / Operation completed in under X seconds
  • X COOL's earned
  • MAX CHAIN of at least X
  • Vitals did not drop below X
  • No mistakes (misses) / <X Misses
  • No Healing Touch
  • Fewer than X blood pools

Some more are:

  • <X diverticulum formed (Tetarti only)
  • Pus formed less than X times
  • Thrombus did not regenerate
  • Core merged less than X times (Bythos only)
  • Red vein not touched (Aletheia only)
  • Membrane regenerated less than X times (Triti only)

There are several known criteria for getting the full 2000 Special Bonus points in Under the Knife, though. These criteria are found in most of the missions in the game.

  • No misses
  • No Healing Touch
  • Complete within a certain time limit