Here's more info; the sizing information from 3 different sources for the same product:

Amazon:
Size Waist (in)
Small 28-30
Medium 32-34
Large 36-38
X Large 40-42
XX Large 44-46

Competitive Cyclist:
Size Waist
S 26-28
M 29-31
L 32-36
XL 37-39
XXL 40-42
XXXL 43-45

Castelli's web site (converting to inches):
Size Waist
S 31.5
M 33.1
L 34.6
XL 36.6
XXL 38.6
XXXL 40.6


Quite a difference in sizes for the same product; I wonder why. As it is, I have a 38 in waist and have the XXL, so by the Castelli size chart, this should fit, and it does except that it is short in the body. I am 6 ft tall, so not an unusual height. Perhaps the typical Italian is shorter in the body than the typical American? If you are short in the body, or just short, maybe the length will not be an issue.