This study reports the results of a long-term cost effectiveness analysis of riluzole in the treatment of amyotrophic lateral sclerosis (ALS) in the United Kingdom. Long term analysis was carried out using Markov modelling extrapolating the transition probabilities derived from clinical trial data. The implications of life extension offered by riluzole were assessed in terms of the time spent in each health state which ALS patients experience. This data was taken from a cohort of 954 patients drawn from a large randomized, double blind, placebo controlled, multi-center trial between 1992 and 1994. RESULTS: Findings suggest that riluzole is effective in prolonging life and that a larger proportion of patients treated with riluzole will stay longer in states where functional status is least impaired. The additional life expectancy of the intervention over the three-year period suggests that treatment of three patients for three years would result in obtaining one additional life-year. Riluzole offsets approximately half the additional costs of treatment through extending the time that patients spend in the milder phases. Therefore, cost per unadjusted additional life-year gained was estimated at £8,587 over the expected lifetime of ALS patients. The findings also show that incremental cost figures are not sensitive to the cost of health states.