Well, a lot of things mentioned about Greg growing up. Zygotes are mentioned, of course, but even GREG doesn't know what those are, and neither should kids (they aren't supposed to). Yes, the book centers around puberty, and it is mentioned (if your kid doesn't know what that is, I don't recommend). Greg also wishes to play spin the bottle, but of course he DOESN'T. He was invited to a party, but he didn't go and based on his friends there wasn't any inappropriate stuff. A teacher says posterior (they don't know what it is until they look up it's meaning is "butt"). A bare butt is drawn for a boy at the urinal. (Trust me, it's not as bad as it seems). A butt is slapped, (it's a picture Greg drew in a book), but it's really not as bad as it may seem. Potty humor, of course, is mentioned all throughout the book. At one point the book mentions Greg's grandfather smokes, but Greg says he won't smoke. (That's a GOOD message). Laughs are all throughout and I think it's very, very good!