In the period 1984-1993, we carried out an incidence and prevalence study of motor neuron disease in Coastal and Mountainous Regions, Croatia. This was the first epidemiological study on motor neuron disease in Croatia. A total of 22 incident cases were identified. The crude annual incidence rate was 0.68 (95% confidence interval 0.43-1.03) per 100,000 person-years; 0.95 (95% confidence interval 0.60-1.43) per 100,000 person-years for men and 0.42 (95% confidence interval 0.26-0.63) per 100,000 person-years for women. The rate adjusted to the European population was 0.63 (95% confidence interval 0.39-0.95) per 100,000 person-years. The age-adjusted incidence in our population is similar to the rates, standardized to the European population, observed in Italy, but lower than recent rates in the US and northern European studies. On 31st December 1993, there were 18 prevalent cases. The prevalence adjusted to the European population was 5.24 (95% confidence interval 3.10-8.28) per 100,000 population. 1 Rates per 100,000 person-years. Coastal and Mountainous Region population estimates for 1993, 21991 Croatia total population as standard. 3European total population as standard. European Journal of Neurology. Vol4 1997 379 R. ZWADINOV ETAL of demonstrating a significant trend based on only 22 incident cases is very low.The prevalence of MND in the Coastal and Mountainous Region, Croatia age-adjusted to the European population, was 5.24 (95% C.I. 3.10-8.28) per 100,000 population.The prevalence for females, ranging from 2.5 to 3.0 per 100,000, reported in other recent epidemiological studies on MND (Granieri et Annegers et al., 1991;Dean et al., 1994) is similar to the prevalence found in this study, whereas the prevalence for males, which, in the studies cited above, ranges from 3.91 to 5.4 per 100,000, is markedly lower than the prevalence calculated for Croatian men (7.96 per 100,000). This may reflect the longer survival times in men than women in this study. Neurologica Scandanavica, 6 7 , 4 1 4 7 . Proctor SP, Feldman RG, Wolf PA, Brent B and Wartenberg D (1992) A perceived cluster of amyotrophic lateral sclerosis cases in a Massachusetts community. Neumepidemiology, 11, 277-281. Reed DM and Brody JA (1975) Amyotrophic lateral sclerosis and parkinsonism-dementia on Guam, 1945-1972. I.