The objective of this study is to validate the Spanish translation of the Inflammatory Bowel Disease Questionnaire (SIBDQ) on ulcerative colitis and Crohn's disease by assessing its convergence validity, discriminatory power, reliability and sensitivity to change. For that purpose, 211 patients with inflammatory bowel disease (116 with ulcerative colitis and 95 with Crohn's disease) completed the SIBDQ, the Psychological General Well-Being Index and the EuroQol. SIBDQ was repeated in those patients who remained in stable remission and in those with changes in clinical activity. Clinical activity was assessed by the Rachmilewitz and Harvey-Bradshaw indices. Correlations among scores of SIBDQ, EuroQol, Psychological General Well-Being Index and clinical indices of activity were all positive and comparable for both diseases (r = -0. 50 to r = -0.70, p < 0.01). Analysis of variance showed that SIBDQ discriminates between different clinical degrees of activity. Cronbach's alpha was 0.96 in ulcerative colitis and Crohn's disease. SIBDQ was also highly reliable when it was repeated in clinically stable patients with ulcerative colitis (intraclass correlation coefficient = 0.82) and Crohn's disease (intraclass correlation coefficient = 0.86). SIBDQ was sensitive to clinical changes in ulcerative colitis and in Crohn's disease, whether patients entered remission (effect size -1.88 and -1.81, respectively) or relapsed (effect size 1.70 and 8.04, respectively). In conclusion, the Spanish version of the IBDQ has proven to be a valid, reliable and sensitive instrument to detect clinical changes in patients with ulcerative colitis and Crohn's disease.