Runners frequently become addicted to running and continue to run even when it is detrimental to their health. In the present study a paper and pencil test to measure running addiction, the running addiction scale (RAS) was constructed and evaluated and used to investigate the psychological correlates of running addiction. The RAS, symptom check list, locus of control scale, commitment to running scale (CR), and a questionnaire about the individual's running habits and degree of addiction were administered to 32 male and 15 female runners. The results suggest that the RAS is reliable and valid, correlating with self-rated addiction. The CR score was correlated with self-rated addiction for males but not for females suggesting that the RAS and CR measure different characteristics and that for female runners commitment to running can occur without addiction. Large gender differences were found in the correlations between the RAS, CR, run frequency, and run duration with the personality, mood, and locus of control scores. Running addiction was found to be associated with high frequency of running and with positive personality characteristics but not with mood enhancement, while the duration of running was found to be associated with mood enhancement. These results suggest that the benefits of running to mood may be obtained without addiction.