A cyclist's helmet incorporates a dome shaped top wall structure, opposite side wall structures, a front opening for forward viewing, a lower front wall structure which extends forwardly and a rear wall structure. It also includes:(a) a frontward facing air inlet means defined by said wall structure, and an air outlet means defined by said wall structure generally rearwardly of said lower front wall structure, and(b) passage means in said wall structure including said side wall structure to receive air inflow from said inlet means for circulation to the upper interior of the helmet and subsequent flow via said wall structure and to said outlet means,(c) said inlet means, passage means, and outlet means located to enhance cooling air flow through the helmet.