Bought this helmet a few years ago, thought that a medium would fit but after a few rides, decided to try a large. It's been kept in the box in the bag with the tags (LS2 sticker is still in the bag!), but the box is no more. Definitely a size M. I've got two other helmets (summer and winter) so it's time for this to go. Only worn maybe 4 times, relatively short rides. Lining is washable.