This study presents the validation of Spanish version of Why worry? Questionnaire which assesses a variable of process related to the overestimation of the positive and negative consequences of the excessive and uncontrollable worry that is characteristic of Generalized Anxiety Disorder. 833 participants from Tenerife (Canary Island) completed this questionnaire among other psychological measures. The exploratory factor analysis yielded a two-factors structure that explained 41.34% of the total variance; both of them showed adecuate internal consistency (alpha 1 = 0.86 and alpha 2 = 0.85) and test-retest (r 1 = 0.70 and r 2 = 0.75) reliability coefficients. A confirmatory factor analysis confirmed two-factor structure. As expected, concurrent validation uncovered substantial correlation with anxiety and mood disorders. The results support a good discriminate validity. The Spanish version of why worry questionnaire provides a reliable and valid instrument, which we can use in cross-cultural studies on worry as a GAD characteristic.