The aim of the present investigation was to develop an instrument assessing the content and the structure of athletes’ self-talk. The study was conducted in three stages. In the first stage, a large pool of items was generated and content analysis was used to organize the items into categories. Furthermore, item-content relevance analysis was conducted to help identifying the most appropriate items. In Stage 2, the factor structure of the instrument was examined by a series of exploratory factor analyses (Sample A: N = 507), whereas in Stage 3 the results of the exploratory factor analysis were retested through confirmatory factor analyses (Sample B: N = 766) and at the same time concurrent validity were assessed. The analyses revealed eight factors, four positive (psych up, confidence, anxiety control and instruction), three negative (worry, disengagement and somatic fatigue) and one neutral (irrelevant thoughts). The findings of the study provide evidence regarding the multidimensionality of self-talk, suggesting that ASTQS seems a psychometrically sound instrument that could help us developing cognitive-behavioral theories and interventions to examine and modify athletes’ self-talk.