The Young Mania Rating Scale is the most widely used tool for the assessment of the intensity of manic symptoms. Unfortunately, to date, there was no Spanish validated version available. This study validated the Spanish version of the YMRS. A sample of 541 DSM-IV manic or hypomanic bipolar patients were recruited in 56 different psychiatric settings in Spain and assessed with the YMRS by 112 clinicians specifically trained in its use on days 1, 7, 14, 30, 45 and at 3 and 6 months. The mania subscale of the Clinical Global Impression for Bipolar Disorders was also performed in order to have a standard measure to compare our results. Feasibility, reliability, validity and sensitivity of the YMRS were analysed. The YMRS Spanish version showed reliability index of 0.88 (internal consistency) and 0.76 (test-retest reliability), and good internal validity and external (p < 0.001) when compared to the mania subscale of the Modified Clinical Global Impression. The results also showed good sensitivity and feasibility. The YMRS Spanish Version is a useful, valid and reliable tool for the assessment of manic symptoms.