The institutional changes which took place with the law of industrial accidents of 1900 and the later regulations caused substantial changes in the Spanish insurance market. A new insurance field was created in which both specialist Spanish companies and foreign insurance agencies operated. This article aims to analyse the evolution of this new field, industrial accident insurance, from its beginning to the 1940s, when it become the most important insurance category. For that purpose premiums and companies have been reconstructed. It is observed too how from the start some industrialists understood the necessity to participate in this business and therefore they sometimes allied with insurance businessmen to form specialist companies. The interest in industrial accidents insurance increased during the 2nd Republic due to government's obligatory insurance requirements, what originated an uprising competition between mutual employer's associations and insurance agencies.
