CG had it right. Castelli redid their sizing last year. In 2008 and later Castelli, I wear a medium. In their earlier stuff, I need a large to accomodate my bust. In other brands (Pearl, Primal, Fox, etc.), I consistently wear a medium. My castelli jerseys are cut closer than my Pearl ones, more of a race fit, especially across the bust. It's also a little shorter than my Pearl stuff.