We will travel around Italy for several weeks in September and would like to try some good restaurants when we are there. I would prefer not to have to take a jacket. Can I wear a nice long sleeved shirt and not look underdressed?

Yes

Sorry! The dress code mandates a coat and tie. Sometimes a turtle-neck shirt is accepted. Buy a light weight summer jacket, silk would be best. Seersucker is an option. Longsleeved shirts are winter wear.
Query your retaurant about dress. Please tell us your experience.

"The dress code mandates a coat and tie"

Complete codswallop. Totally untrue. She's making this nonsense up as she's going along.

Personally, I've never found any restaurant in Italy, at any level, with anything so absurdly provincial as a dress code: apart from anything else, most of Italy's hot for much of the year and having air conditioning isn't essential to being a restarant that takes cooking food seriously. But putting their customers' comfort, as opposed to their own self-importance, is.

Fellow-diners expect you to dress smartly - but in Italy, you can be far smarter in the right jeans than any jacket-wearing hick from the backwoods of North Dakota.

Now the poster might be visiting a restaurant that DOES have a code. Again personally, I'd dismiss any such place in Italy as tourist-centred and therefore not serious about proper food. But the ONLY place you'll find that out about a specific retstaurant is by asking it, rather than relying on the bizarre inventions of misguided Fodors posters.

Ah, flanneruk, cranky owing to the Tory victory in Crewe, are we?

Pretty soon it will be neckties everywhere in the UK again and black jackets, striped trousers, bowler hats, and rolled umbrellas in Whitehall.

Shirtsleeved Guardian readers will have to escape abroad to feel appropriately dressed.

Not many woods (back or front) in North Dakota, flanner.

Yes many restaurants accept American casual diners. That said; my wife has an elegant, new 'small black dress' and her mother's pearls and she wants to wear them in an appropriate venue. Will I look alright in shirtsleeves?

having visited several nice restaurants in Rome , I have seen all kinds of dress.
Older ( Italian ) men in suits, women in nice dresses, tourists in various outfits - from jackets to short sleeves, open neck shirts etc.

Mind you, these were not restaurants in the Hilton or the Eden. If that is where you are heading, better ask.

GSteed; Seersucker or a silk jacket for men???

As long as you wear long trousers and a shirt with a collar you will be ok anywhere. No shorts, tshirts or white sports shoes in the evening.