Prebisch arrived at ECLA for the first time in 1949, to write a report in which he set out his views on the main problems then facing the economic development of Latin America (Prebisch, 1949);. As he had been hired as an outside consultant, he did not receive the support of other members of the institution in its preparation, nor did he have much time at his disposal, so that the report was a reflection of the ideas he already held prior to joining ECLA. As the content of that work made a great impact on academic and political circles in the region and came to be considered one of the basic pillars of structuralist thinking, it has often been wondered when and why Prebisch incorporated those ideas into his thinking. In 1949 Prebisch already had a lengthy career as an academic and public official behind him and was, according to Furtado, "the only Latin American economist with an international reputation" (Furtado, 1985, p. 58);. His first works date from the1920s, and the general opinion is that in those years he was a firm supporter of neoclassical ideas, but there is very little in them that could have served as a basis for the 1949 report, and only as a result of the crisis that began in 1929 does he appear to have begun to abandon his neoclassical views and to look for new interpretations of the economic process and heterodox policies for reshaping it. The fact that Prebisch often confirmed this simple division of his thinking into two periods must have been one of the main reasons why this was accepted without question and a deeper study was not made of his thinking in the 1920s (Prebisch, 1983);. Attentive reading of the material he wrote during those years, however, shows that the continuity of his ideas was much greater than has been assumed, so that it would be very simplistic to divide the evolution of his thinking into two periods -orthodox and heterodox- separated by the 1929 crisis. Prebisch himself, when going into greater detail, recognized that the 1920s had not been a period of pure orthodoxy for him. For example, when referring in an interview to the first articles he had written, he said "In those articles I tried to interpret actual phenomena with my own eyes, and not with economic theories from outside. I attached great importance to the balance of payments... I began to understand Argentina's external vulnerability at that moment. This was between 1921 and 1923" (González and Pollock, 1991, p. 458);. The fact that Prebisch often confirmed this simple division into two clearly opposed periods must have led those who have studied his thinking to take this for granted, with the already mentioned result that they did not study his thinking during the 1920s in greater depth. The aim of this article, therefore, is to show that even from his first works, written in 1920, Prebisch began to shape the body of ideas that he formulated as a whole when he arrived at ECLA in 1949, and also that he did not need to go through the experience of the 1929 crisis in order to become aware of the defects of the primary export pattern, since these had already been clear to him even in the early 1920s, when the Argentine economic process was considered a shining example of successful growth. The brutal impact of the crisis merely served to confirm to him that he had not been mistaken about those defects and to lead him to definitively abandon his confidence in the Gold Standard as a basic criterion for economic policy management and seek new ways that would permit an improvement in the standard of living of the population.