OBJECTIVES Mobility impairments affect most multiple sclerosis (MS) patients (93%), yet many patients (~40%) “rarely or never” discuss trouble walking with a healthcare provider (HCP).  To facilitate patient-HCP dialogue and early identification of mobility impairments, the Early Mobility Impairment Questionnaire (EMIQ) was developed based on qualitative research with patients diagnosed with MS and in collaboration with key opinion leaders.  To minimize the burden associated with administration of the EMIQ, psychometric analyses were applied to the initial draft to produce a parsimonious yet robust instrument.  METHODS The EMIQ’s psychometric performance was evaluated in a multi-center, prospective, observational study in subjects with an Expanded Disability Status Scale (EDSS) score of 2.0 to 6.0.  Iterative exploratory factor analysis (EFA) was used to guide item reduction; subsequently, an item response theory (IRT) graded response model was applied to confirm the robustness of the instrument.  Logistic regression analyses (using EDSS scores) were used to confirm discriminatory power. RESULTS In total, 124 subjects with moderate MS (EDSS mean score = 4.2) were included in the study.  Discriminant validity, factor analysis, and IRT modeling identified six items for reduction.  The resulting 9-item scale had one strong underlying domain (first eigenvalue explained 60% of variance).  The information curve showed sufficient sensitivity (I>3.3 for -2.6≤θ≤2.4) throughout the scale (mild to severe), with the most precise information provided at ½ SD above the mean (I=12 at θ=0.4).  Logistic regression showed that the EMIQ was able to discriminate between patients with and without walking impairment (p<0.05). CONCLUSIONS The psychometric analyses resulted in a streamlined scale that is appropriate for the screening of subjects experiencing early mobility impairments due to MS.  In addition to a potential role in guiding clinical assessment and intervention, the EMIQ may also prove useful in the longitudinal assessment of mobility, as patients’ conditions decline.