In clinical trials drop out bias reduces the validity of results. This is a particular problem in long-term multiple sclerosis (MS) studies, particularly when patients become progressively disabled and have increasing difficulty attending assessment clinics.To assess the validity of nurse led telephone assessment of Expanded Disability Status Scale (TEDSS) in MS patients with EDSS scores >6.0.We performed a multi-centre, single blind trial to assess nurse derived TEDSS against physician face-to-face EDSS scores derived from neurological examination (FEDSS) in patients with clinically definite MS and EDSS >6.0.Ninety patients (n=15 primary progressive MS, n=74 secondary progressive MS, n=1 relapsing remitting MS) had a mean baseline FEDSS of 7.5. TEDSS correlated with FEDSS (r=0.76, p<0.0001) and kappa scores for perfect agreement, within 0.5 of an EDSS points, and within 1 EDSS point were 0.25, 0.86, and 1.0 respectively. Intra-class correlation between the scoring systems was 0.88, representing a high level of agreement.Nurse-led telephone assessment of EDSS gives good agreement with physician derived face-to-face EDSS in MS patients with higher disability scores. This may be a valuable tool to improve clinical follow-up in routine clinical practice and improve patient retention in long-term outcome studies.