Macaroni is a type of pasta. Pasta can be for example: spaghetti, tagliatelle, penne, tortellini, ravioli and many other dishes with a dough base and ingredients similair to the examples of pasta I gave. In countries like the USA it is very common to eat macaroni or spaghetti with ketchup. In Italy, however, you curse their cuisine when you do that. Pasta is mainly eaten with tomato sauce with some other ingredients, such as: onions, basil or meat. Though, I leave this question for a real expert with the Italian cuisine.

You should ask in the English section: "macaroni" it is not an Italian word. I guess it is used as a synonym of "pasta" in English language, probably a synecdoche (a specific object for its class). In Italian, "maccheroni" is only the name of a type of pasta, as other dozens and dozens are. Also known as "rigatoni", they are tubes of pasta with about a lenght of four cm. and a diameter of one cm. You can say one of them here among of some other types of "pasta corta" (short pasta): http://upload.wikimedia.org/wikipedia/commons/7/7d/Pasta_2006_2.jpg And some other types of "pasta corta", here: http://upload.wikimedia.org/wikipedia/commons/2/2b/Pasta_2006_3.jpg Some kinds of "pasta lunga" (long pasta), here: http://upload.wikimedia.org/wikipedia/commons/9/99/Pasta_2006_1.jpg http://upload.wikimedia.org/wikipedia/commons/e/e7/Pasta_2006_5.jpg http://upload.wikimedia.org/wikipedia/commons/4/4c/Pasta_2006_6.jpg And some kinds of "pasta da brodo" (pasta for soup), here: http://upload.wikimedia.org/wikipedia/commons/c/c1/Pasta_2006_4.jpg Ketchup is not popular as a condiment for pasta at all. Anyhow, tomato sauce, that is very similar to Ketchup in its appearance (but not in its composition) is the most used among the condiments. About other sauces for pasta, Andrew was very exaustive. I can add anchovies sauce ("bigołi in salsa"), duck ("bigołi co l'arna"), clams, mussels, tripe and, only for the brave, "pajata".

Based on my experience, no one in the US eats pasta with ketchup, except maybe little children. While it doesn't taste nearly as good as it does in Italy, we eat it with the same kinds of sauces, with tomato-based being the most common, either with or without meat, usually beef.

=== Let me add something === A couple of fundamental tips (in my view) about Italian sauces, if you want to experiment by yourself: a) always use 'olive oil', possible of a very good quality. b) when cooking with the olive oil (ad esempio: preparare il soffritto), never let the oil make make smoke, which thing would happen if the temperature raises over 200 Celsius degrees (more or less) and the oil molecules begin to crack into components which are very very heavy for the liver and even toxic (acrolein), in this case even ketchup would be healtier, although not tastier! When I fried soemthing, sometimes I add slices of carrots or potatoes in the oil, (something that will very slowly add tiny anmounts of water in the pan and that will not alter the taste) so to stop the possibility for the oil to reach the 'smoke point'

I ate pasta with ketchup just once in my life in Italy and never in the United States. We add to pasta several kinds of 'sauces' (salse e sughi), a very easy but still tasty is this: -- some leaves of sage (Italian: salvia) must be cooked with olive oil or butter, or a mix of the two. -- have ready some 'grated cheese', we use parmigiano or 'grana padano' or 'pecorino'. -- when the pasta is cooked mix all the stuff. Other things we add are (those are popular in all Italy) : - pesto di basilico, olio di oliva, pinoli, (noci) (recipe from Genova) - ragu` (from Bologna) - salsa di pomodoro con burro - aglio (garlic) olio e peperoncino - lasagna con ragu` e besciamella (this is not a sauce, but the name of a very special 'pasta' dish) - zucchine taglaite a fettine e fritte nell'olio, con aggiunta di parmigiano a fuoco spento - pasta alla 'carbonara' (very tasty, quite nutritive also) - pasta con bottarga di muggine e sedano e altre verdure. - pasta alla Matriciana (Abruzzo, Roma) - pasta al limone. - pasta con melanzane, zucchine, peperoni, cipolla e altre verdure. We are talking about the language here, so I only assure you that they do taste good if the cook is clever enough, and I believe that you might easely find the recipes on a book or searching the Web.