The following paper presents the original tithe series for the province of Guadalajara in central Spain. The new series contribute to recent debates on pre-modern economic growth, thus improving knowledge of a key region of Spain. The study includes analysis of the four main grains, wheat, barley, rye and oats, and the evolution of their production during the eighteenth century. The series complete previous estimates of grain production for New Castile and suggest that this was a period of growth. However, the increase was not a sustained process but one with intense imbalances, with production reaching its peak in the mid 1750s followed by a deep crisis and very weak recovery. Wheat was clearly the most important of the four grains in volume and especially in value. Its predominance was maintained thanks to a demand encouraged by the demographic growth that took place during the eighteenth century. The production of wheat was also the most stable, followed by barley, oats and rye, as might be expected given that the grain was usually cultivated in the most fertile lands. A comparison with other tithe series from the interior of Spain reveals similarities, such as the crisis of the 1760s, but also different recuperation trends. The findings indicate that Guadalajara followed a growth pattern characteristic of a traditional economy in the interior of Spain.