The demand for triathlon has increased considerably during recent years; however, up to now there is little research available on the economic aspects of this sport. Therefore, the purpose of this study is to investigate the sport-related expenditure of triathletes. Based on the concept of consumption capital, a theoretical framework is presented that explains sport-related expenditure. Quantitative data were collected using a nationwide online survey of active triathletes in Germany (n=786). Yearly sport-related expenditure amounts to €2745 on average. Regression results show that consumption capital (years of participation, weekly time of practice, self-assessed level of performance, and participation in triathlon competitions) and socio-demographic characteristics (age and income) are significant drivers of sport-related expenditure. The findings have implications for the management and marketing of triathlon and related products (e.g. tourism) because of the increasing number of participating triathletes who represent an economically interesting target group.