This study was designed to test the effects of mental preparation and trait anxiety level on the motor performance of a group of rugby players. The Sport Competition Anxiety Test (Martens, 1977) was administered to subjects to assess their trait anxiety levels, and a proportion of these subjects performed two experimental tasks consisting of a strength task and a running speed and skill task. Mental preparation was found to significantly increase motor performance of low and medium trait anxiety subjects in the running task, but had no effect on the strength task. For the high trait anxiety group there were no differences due to mental preparation in the running task but motor performance was significantly worse in the strength task. It was concluded that the difficulty and unfamiliarity of the strength task was itself a source of arousal, and that when coupled with mental preparation arousal was above the optimum and motor performance did not improve. The implications for coaches and players of all sports are discussed, and suggestions made for producing optimal performance through pre-competitive mental preparation.