Motor neurone disease (MND) is a useful paradigm for many progressive disabling neurological disorders and serves as a particularly apposite model for the study of patients' responses to progressive and irreversible disability. We studied the progression of disability and the patients' perception of their health in a group of MND patients ( n = 14) for 6 months from diagnosis or soon after. A comparison group of similar age, gender ratio and initial disability on Barthel index were Parkinson's disease (PD) patients, admitted because of poor response to outpatient drug therapy and increasing disability ( n = 22). MND patients showed rapid deterioration in all aspects of self care and mobility, as assessed by Barthel Index. 32% PD patients showed a significant improvement in disability during their admission. For both groups, perception of their physical health on the SF36 was very poor at recruitment compared to age- and sex-matched population norms. However for patients in both groups the SF36 could not be used to monitor changes in perception of health because of floor effects. In those in whom change could be assessed, there was a trend for MND patients to deteriorate and PD patients to improve. We conclude that loss of independence in self care and failing mobility may occur more rapidly than current medical and social services can accommodate. There is a need for planning and proactive intervention to support patients and carers. The patients' perception of their physical health is poor from time of diagnosis as assessed by the SF36, but this scale cannot be used to monitor patients with MND or late stage PD over time.