The aim of this study was to assess the trend of motor neuron disease mortality in Spain from 1990 to 2005, and to ascertain the existence of geographical differences in mortality rates. MND deaths are registered by the National Statistics Institute of Spain – International Classification of Diseases (ICD) codes ICD9 335.2 (1990-1998) and ICD10 G12.2 (1999-2005). Annual sex- and age-specific rates, as well as rates adjusted for the standard European population were obtained. Provincial standardized mortality ratios (SMRs) were calculated for the study period. Respective provincial SMRs were smoothed with data from adjacent provinces using a Poisson model. Results showed that MND mortality increased in Spain from 1990 to 2005. Geographical differences between provinces were evident throughout the study period. In general, risk of death due to MND was higher in regions lying to the north of Spain. In conclusion, the temporal and geographical variability observed might be explained by genetic factors, differences in environmental exposures and the possible influence of the type of medical care and treatment received. Mortality depends also on health service quality and diagnostic validity. All these factors may play a very important role in analysis of MND mortality in Spain, and the contribution of each of these will have to be examined in depth by ad hoc studies.