Shock is usually a negative thing - a sudden piece of news that makes you sad, angry, upset. Surprise can be a positive or negative piece of unexpected news - a surprise birthday party, a sudden meeting with someone you have not seen for some time. This is the main difference. One is negative and one can be negative or positive.

''Shock'' is used almost by journalist for strong effect on last news, about bad news; it is a word used for thing sudden, unexpected, with many and dangerous aftermath and effects on moment. Instead, a ''surprise'' is a simple news, it can be like a gift, a present, almost good news, for exaple a party organizated for a friend's birthday. It's a important and strong difference about meaning between this two words.

If, by any chance, you read a sort of joke that has the punchline "Madam, _I_ am 'surprised;' _you_ are 'shocked,'" say so. This joke is about an _outdated, old-fashioned_ point of usage and does not really refer to modern usage at all. If you are not asking about this joke, ignore this posting.

You can have a pleasant surprise. A birthday gift can be "a surprise." A surprise is anything you do not expect, good or bad. The recent stock market drop in the United States came as a surprise to me. "Shock" can literally mean a violent collision, or impact. Thus, we speak of the "shock" of an earthquake or an explosion, or an "electric shock." Therefore, "shock" can mean a surprise, almost always bad, that is so strong that it feels to you as if something had hit you--like an earthquake, an explosion, or a bolt of electricity.