the purpose of this study was to assess the effects of three types of thought patterns; positive thoughts, mood words, and task-relevant content, on swimming performance in age group swimmers. the major dependent variable was the time it took subjects to perform each 100 metre segment of two 400 metre constant-effort swims and the time taken for each 100 metre repeat in a set of eight 100 metre swims. a single subject analysis of performance data emphasized the importance of the use of thought factors in improving swimming performances. all subjects (n = 6) improved in at least two of the three treatment conditions over normal thinking in each of the two performance tasks while three subjects improved in all treatment conditions. group averages indicated that task-relevant content was the most effective variable while mood words, and positive thinking followed in order. the effects of the treatment conditions across the group for both performance tasks were significantly greater than one would expect by chance alone (alpha = .05). the results of this study supported the importance of the thought content for improving performance outcomes in the swimming training environmento the need for more emphasis on mental training components in training athletes was supported.