There are few studies on patient knowledge in multiple sclerosis (MS), and only two published questionnaires. The objective of this article was to develop and validate the MS Knowledge Questionnaire (MSKQ), a self-assessed instrument for newly diagnosed MS patients. Thirty multiple-choice statements, conceived to test MS knowledge, were produced by a multidisciplinary panel and pre-tested on three MS patients, resulting in an intermediate 26-item version. This was tested on 54 MS patients for internal consistency, content and construct validity (validation sample I). The final (25-item) MSKQ was a primary outcome measure in the SIMS-Trial on an information aid to newly diagnosed MS patients. Postal responses of SIMS-Trial participants to the MSKQ a month after intervention (validation sample II) were analysed. Median MSKQ scores in validation samples I and II were, respectively, 18 (range 9-23) and 17 (range 3-24). Acceptability, internal consistency (Kuder-Richardson-20 formula 0.76) and content validity were good. Educational attainment and receiving the information aid were the main independent predictors of MS knowledge. Other predictors were female sex (positive association) and disease duration (negative association). In conclusion, the MSKQ has good clinimetric properties and is sensitive to an educational intervention. We propose the MSKQ as a brief instrument for clinical practice and research.