A review of the United Kingdom (UK) multiple sclerosis (MS) literature suggests that over the last three decades prevalence and estimated incidence rates have increased, while mortality rates have been declining. UK mortality data over a 30 year period have been studied to examine temporal and geographical variations, to estimate changes in survival, and to examine the relationship between mortality and morbidity trends. The study has shown an overall decline in mortality throughout the UK of approximately 25% over the 30 year period ending in 1983, and a reduction in the mortality differential between Scotland, and England and Wales, but no positive correlation has been found between mortality and morbidity. The overall decline in death rate in females was 23% and in males 30% over the 30 years of the survey. The total number of deaths declined by 39% between the five year periods 1954-58 and 1979-83 in Scotland compared with a 10% decline for England and Wales. Estimated median age of death increased from 52 to 59 years and the improvement in survival over the period of study was similar for both countries and is unlikely to have contributed to the reduction in mortality differential. Within England and Wales regional mortality rates did not show a clear north-south gradient. The decline in the mortality differential between Scotland and England (if not artefactual) may provide an important aetiological clue in the search for the cause of multiple sclerosis, and the rate of decline suggests an environmental rather than a genetic aetiology.