Some methods of stable and quasi-stable population analysis recently developed at the Office of Population Research of Princeton University were applied to the problems of inferring levels and trends in the vital rates of the Colombian population during the intercensal years 1938-1951 and 1951-1964. Analysis of census data indicated a gain of 7-8 years in life expectancy at age 5 for Colombian women between 1938-1951 and 1951-1964 and of about 4 years in the corresponding figure for males. Mortality risks in Colombia had recently been higher than they were in countries such as Brazil and Mexico. Whereas life expectancy at age 5 for males would not be higher than 55 years, even if the male rate of growth for the 1951-1964 period were assumed to be equal to the female rate reported, calculations for Mexico indicated a figure of 59 years and for Brazil a figure of about 60 years for the period 1950-1960. With higher mortality in Colombia, and about the same rate of natural increase for the three countries, the implication was a higher level of fertility in Colombia, which seemed to be corroborated when the cumulative age distribution of Colombian males and females in 1964 were compared with their Brazilian or Mexican counterparts in the 1960 census. At all ages and for both sexes, the Colombian data yielded evidence of a somewhat younger population, which necessarily implied a higher level of fertility combated to the other two countries. The results suggested that Colombia was still behind these two other countries as far as the transition in mortality was concerned. A higher level of fertility in Colombia than in Mexico or Brazil, unless counteracted by changes in marriage patterns or in reproductive habits, might lead to acceleration of the rate of growth as mortality declines further.