The current study examined the effects of self-talk on thought content during a tennis forehand crosscourt exercise. 16 adult tennis players (M age = 37.3 yr., SD = 8.31) were randomly assigned to either an experimental or a control group. After completing three baseline assessments, the players of the intervention group developed and implemented self-determined instructional cue words throughout three intervention trials. The participants' thought content was divided into three categories, and repeated-measures analyses of variance indicated a significant group by time interaction for execution-related thoughts and outcome-related thoughts, but not for circumstance-related thoughts. Follow-up comparisons showed that the experimental group players' execution-related thoughts increased and outcome-related thoughts decreased significantly, whereas thought content did not change significantly in the control group. The results of this study provided evidence for the effects of self-talk on players' thought content and supported the idea that self-talk could help athletes to focus on task relevant information.