Drawing from theory on serious leisure, social worlds, recreation specialization, ego-involvement, and travel motivation, it is proposed that many people with specific sport or lifestyle interests will develop event-specific careers. These careers will follow a trajectory that can be measured in terms of six dimensions: motivations (especially the pursuit of higher-level personal needs); changing travel styles; spatial and temporal patterns, event and destination choices. As a partial test of the event-tourist career trajectory, a large sample of registrants for a half-marathon in Sweden was questioned in a pre-event survey about their motives, involvement in their sport, and event-related travel. Employing an involvement scale specific to amateur distance runners, analysis revealed that most runners were not highly-involved in this sport. However, a comparison of the most highly-involved (constituting the top decile of the sample), and the remainder, revealed many significant differences that do support the hypotheses in all six dimensions. Implications are drawn for theory development and future research, as well as for the design and marketing of sport events aimed at niche market segments.