Background. To describe the number of visits (total and per COVID-19) attended by the Spanish hospital emergency departments (EDs) during March and April 2020 compared to the same period in 2019, and to calculate the quantitative changes in healthcare activity and investigate the possible influence of hospital size and regional COVID-19 seroprevalence. Method. Cross-sectional study that analyzes the number of visits to Spanish public EDs, reported through a survey of ED chiefs during the study periods. Changes in healthcare activity were described in each autonomous community and compared according to hospital size and the regional impact of the pandemic. Results. The 66% of the 283 Spanish EDs participated in the study. The total number of patients attended decreased to 49.2 % (< 30 % in the Castilla-La Mancha region), with a 60 % reduction in non-COVID-19 patients (reduction < 50 % only in the regions of Asturias and Extremadura). While there were no differences in changes of healthcare activity according to the size of the hospital, there were differences in relation to the regional impact of the pandemic, with a direct correlation related to the decrease in non-COVID-19 activity (the greater the impact, the greater the decrease; R= 0.05; p = 0.002) and an inverse correlation to the overall activity (the greater the impact, the lesser the decrease; R= 0.05; p = 0.002). Conclusion. There was a very significant decrease in the number of ED visits during the first pandemic wave, although this decrease cannot be explained solely by the local incidence of the pandemic.