What is the absolute best week to stay in Cinque Terre in May/June or September/October?

Go with the earliest in May and latest in October

Tina - I would suggest September. Weather will still be good plus hordes of tourists will not be crowding the area. October might produce rain.

I'd go with the first week of May. June, Sept anf the first half of Oct will be almost as crowded as summer. Late Oct does have an increased risk of rain, which pretty much eliminates any chance of hiking. If you can travel in mid to late April, so much the better.

Early May is not my favorite because it tends to be rainy and can be a little chilly. Our preference is mid Sep to mid Oct. We generally find that time to be fairly dry and since it is following a hot summer the evening tend to be a little warmer and more pleasant.

I was in Cinque Terre from 09/22-09/24 a few years ago. It was still lively but not crowded and the weather was nice. I was there at about the same time a couple of years earlier with similar experience. Crowds are probably unchanged but I can't guarantee the weather.

Edit: By not crowded I meant not extremely crowded the days I was there, but maybe I just got lucky on cruise ships or was hiking when the worst of the cruise ship crowds hit town. Evenings, one stay in Vernazza and the other in Monterosso, were pretty pleasant as I recall.

Now - I've only been twice - in '08 and '12, both times within a day or two of Sept 23 (for 2 nights). The first visit was thru the week, 2nd was over a weekend. I know the crowds had only gotten worse in those 4 years, and they're even worse now. The weekend stay we had - the trains/platforms were crowded, and Vernazza was crammed (we stayed in quiet little Corniglia both times).

My suggestion would be if you can stay on weekdays instead of weekends, it might be less crowded. I'm not sure how far ahead they release cruise schedules, but that could make a diff as well. But the nice thing about staying IN one of the villages is you have the mornings and evenings to yourself when the daytrippers are gone.

As Nicole recommends, definitely avoid Friday and Saturday nights as well as holidays.

We have been to Liguria five times (4 of which we stayed in the Cinque Terre) in October and felt the weather perfect for outdoor activities. Occasionally a bit of rain, sometimes warm enough to eat outdoors at night, crowds lighter at least mid-week.

I’ve been there in September and it was still very crowded but I loved it.

I always go early to mid May. Try, like suggested to go during the week if you can. Even if the cruises come in, if you get out early before them, and come back at dinner time (5 ish) it won't be too bad. Cinque Terre is great at night!
Weatherwise it is a toss-up. I have gotten sunburned, rained on, and had to wear winter clothes. You just never know.

Just listening to the RS podcast and someone asked about CT and he said you could still go in the summer, but try to avoid weekends...but he did say shoulder season was better. (Glad my observations lined up with his about weekends). He also takes some of the blame for CT being overrun...lol.

If you want to listen to it, go to the radio section on this page or if you have a podcast app just look for travels with Rick steves. Other great questions and observations on Venice and Rome off the beaten path.

We were in the CT last year in early May. It poured the whole time we were there. For us, there wasn't much to do in inclement weather. As a result, our 3 days there were the least favorite stop on our 18 day trip. I would suggest the Fall. My brother has beautiful pictures of Manarola in Sept!