Prior to 1964 the Colombian population was rather stationary, with net migration having little effect on the total volume of population. Between the 1963 and the 1973 censuses the displacement of Colombians abroad took place on such a large scale as to have a significant effect on the demographic structure of the country. The deterioration of living standards in Colombia in combination with a lack of economic opportunities, accounts for this mass exodus to countries with stronger economies. A large portion of those who leave establish themselves in foreign countries as illegal aliens. Immigration to the U.S. and Venezuela accounts for 85% of the total migration. Official statistics for Venezuela indicate that there are more than 300,000 Colombians living there illegally, but unofficial sources state that the figure is closer to 2 million. In the U.S. there are more than 25,000 Colombians registered, but a more reasonable estimate of 1,200,000 Colombians living there is closer to reality. The author offers several hypotheses for the increase in the number of illegal aliens to the U.S. These include favorable conditions for legal immigration until 1965, and increasing promotion of tourism to the U.S., with greater opportunity to remain there beyond the visa period. Between 1967 and 1969 new restrictions on immigration were imposed by U.S. authorities, causing a drop of entries into the U.S. After this initial period, however, the number of Colombians coming to the U.S. increased again. This study includes charts which indicate legal and illegal immigration, and deportations. These categories are analyzed on the basis of sex, age, country of destination, and place of origin in Colombia.