It's tough for me to source shoes sized in Euro sizes.  Sometimes a 37 fits, sometimes a 38.  I really wanted the cobalt blue version of these, and Amazon only had the 38, so I took a chance.  When I first put them on, they looked adorable, but felt significantly too big for me.  However, a few hours later I came by and put them on again, this time making sure to close the instep strap as far as I could.  This has helped tremendously and the 38 is definitely the size for me.  I can tell that a 37 would be too small in the footbed.

However, I've come back to edit this review.  After ten minutes of wear, I ended up with crippling pain in the ball of my right foot.  This is the same kind of thing that happens to me with Fluevog's shoes (any with a slight heel), and so, after my terrible months-long search for a pair of Fluevogs that fit (and coming away disappointed), I'm putting these El Naturalistas on the same list.  I am sending them back to Amazon.  I wonder whether the angle of rise (between the toes and the ball of the foot) is too steep, or something like that.