A review of the relevant literature has identified two important areas of sex differences in the field of mathematics. Not only do considerably more boys than girls perform very well in mathematics, but girls, far more frequently than boys, choose not to take intensive mathematics courses once they are no longer compulsory. A variety of factors are frequently cited to explain such consistent sex differences. This paper reports two studies that examine whether there is a relation between fear of success and sex differences in performance and participation in mathematics courses. The evidence provided highlights the effect of environmental pressures. Possible classroom based intervention programs are discussed.