I wear a size 11.5 medium wide in 99% of my shoes. I bought my first Vionics 3 months ago, flip flops size 11.5. Fantastic fit and comfort! My second pair had size 11.5 flip flops. Brilliant! My third was sneakers but 11.5 was too small so I took 12. I returned them after one of the eyelets came loose and the paint inside the shoe soiled my socks. I ordered a size 12 hiking shoe that I am reviewing and my big toe is being pressed against the front of the shoe. All I can say is that the Vionics are a good shoe for the most part, but they do not true to size. If you decide to buy a pair, be prepared to return them until they fit.