The Official Rules of Golf appear on the About.com Golf site courtesy of the USGA, are used with permission, and may not be reprinted without the permission of the USGA.

9-1. General
The number of strokes a player has taken includes any penalty strokes incurred.

9-2. Match Play
• a. Information as to Strokes Taken
An opponent is entitled to ascertain from the player, during the play of a hole, the number of strokes he has taken and, after play of a hole, the number of strokes taken on the hole just completed.

• b. Wrong Information
A player must not give wrong information to his opponent. If a player gives wrong information, he loses the hole.

A player is deemed to have given wrong information if he:

(i) fails to inform his opponent as soon as practicable that he has incurred a penalty, unless (a) he was obviously proceeding under a Rule involving a penalty and this was observed by his opponent, or (b) he corrects the mistake before his opponent makes his next stroke; or

(ii) gives incorrect information during play of a hole regarding the number of strokes taken and does not correct the mistake before his opponent makes his next stroke; or

(iii) gives incorrect information regarding the number of strokes taken to complete a hole and this affects the opponent’s understanding of the result of the hole, unless he corrects the mistake before any player makes a stroke from the next teeing ground or, in the case of the last hole of the match, before all players leave the putting green.

A player has given wrong information even if it is due to the failure to include a penalty that he did not know he had incurred. It is the player’s responsibility to know the Rules.

9-3. Stroke Play
A competitor who has incurred a penalty should inform his marker as soon as practicable.

©USGA, used with permission