Identifying key welfare issues for thoroughbred racehorses could lead to an improvement in standards. A lack of scientific information on the relative importance of key issues was addressed by soliciting the views of, first, welfare experts in the industry and, second, a broader group of stakeholders, who selected the best welfare options by adaptive conjoint analysis. The experts represented racehorse breeders, veterinarians, trainers, owners, government officials, salespeople, farriers, transporters, and horse re-trainers for post-racing activities. In a focus group meeting, the experts identified fourteen key welfare issues, each with two to four levels that related to common husbandry practices. Then, in an internet survey, 224 stakeholders ranked the issues using adaptive conjoint analysis, in declining importance, as: horsemanship > health and disease > education of the horse > track design and surface > ventilation > stabling > weaning > transport > nutrition > wastage > heat and humidity > whips > environment > gear. Relatively uniform responses to the survey by the different stakeholder groups suggested that there was a common view on what had the biggest impact on welfare. An exception was a greater rating given by women than men to the importance of correct horse nutrition. The rating of importance for welfare of different levels of provision of each issue mostly conformed to the scientific evidence, with the exception of weaning. This understanding of the importance of welfare issues for thoroughbred racehorses could be used to target interventions to the most serious problems.