When to visit?

It really depends what cities you want to visit. Rome may not seem bad at 87 but the humidity is high. Plus you probably don't spend all day outside walking around in your heat, you're probably going from a home with a/c to a car with a/c and then to work with a/c. If you plan on visiting coastal cities it's the perfect weather for the beach!

Thanks for the responses. :)

I'm outside quite a bit and go camping/hiking a lot but I guess spending most of the three weeks outside would get the best out of us. Rome will be our southernmost destination so the rest of the trip should be slightly cooler and we'll miss the Amalfi Coast crowds. Most of the time I will be in the cities and Tuscany but with some swimming (CT, Venice, Siena). Speaking of which, does anyone know if there are some good scuba diving and/or snorkeling opportunities around the Cinque Terre and Siena?

But if the crowds and costs aren't drastically different, I guess I'll probably go with May and June. Thank again.

July and especially August are the peak holiday months for Italians and other Europeans. However, because of the heat they will be heading for the coast, countryside, lakes and mountains leaving the cities relatively quieter. That's why you will see that city hotel prices are usually lower in August.

We have been to Italy twice - the first time in May to Rome and other parts of Italy, the second in October, to Rome only. Both times there were lots of tourists in Rome and other places - e.g. Cinque Terre. I don´t think you can avoid tourists in a place like Rome. As for the heat - we are Australian so high 80´s doesn´t bother us much either.

Of the times you can go, I would choose mid May to the end of June - slightly lower temps and still lovely long days.

"...the average daily high in July is 87 in Rome. Am I missing something? This seems perfect. Where I live, in Utah, July is 100..."

If you are outside walking most of the day on those hundred-degree days in Utah and think it's fun, then you'll probably not mind Rome in July/August.

Here in Arkansas it was between 95 and 100F every day for the last month, with high humidity, and I did just fine because I'm usually moving just the short walk between an air conditioned car and my air conditioned house or office.

But in Rome last month we were all miserable on 90-degree days because we were outside all day, with pretty much no breeze, pretty much no shade, walking on hot city streets and "old piles of rocks". The heat and humidity just wears you out after a few hours, and there's no relief until you get back to the hotel where you can get some air conditioning or at least a fan.

Stopping at a café for a beer in the shade can help re-energize you (unless you're Mormon, in which case make that something non-alcoholic), but the affects wear off quickly after you start walking again. In the Forum/Palatine Hill there's not much shade or water, and the Colosseum's not much better.

Go in May. Not only is the weather nicer, but Italy is beautiful in May because so many of the flowers are in bloom.

Of the two, I'd go in May.