The object of this project was to study the fertility and mortality of the people of Puerto Rico. It was found that fertility is very high and has been consistently high since 1900. It was found that mortality has declined very rapidly since 1900. Hence, the combination of these two trends is bringing about a very high rate of natural increase and making Puerto Rico one of the most densely populated areas in the world. Fertility was studied in relation to certain cultural and demographic factors such as age at marriage, length of the childbearing period, age distribution of the population, percentage of illiteracy, and occupational status. From this, it was found that: 1. Most Puerto Rican women marry at very early ages. 2. The child-bearing period is long and characterized by high-age-specific birth rates. 3. Puerto Rico's population is mostly composed of young people, with 74.6 percent under 35 years of age, reflecting a high fertility for the present and future. 4. There is a high percentage of illiterates and persons with little schooling, both of whom have higher fertility rates than highly educated persons. 5. Almost 40 percent of Puerto Rico's employed persons are laborers, who have higher fertility rates than other occupational groups. Fertility also was studied in relation to selected regional characteristics. From this, it was found that: 1. The highest fertility ratios are in the most rural regions. 2. The three regions with the highest fertility ratios have the highest percentage of young persons reflecting a high fertility for the present and the future. 3. The three regions with the highest fertility ratios have the highest percentage of laborers. 4. The region with the lowest fertility ratio has the highest percentage of females. Mortality is being affected by advances in medical science, public health, and improvement in the level of living. Life expectancy has increased from 38 years in 1900 to 61 years in 1950, mainly as a result of the decline in mortality. The five leading causes of death are tuberculosis, diarrhea enteritis, diseases of the heart, pneumonia, and cancer. Malaria was a leading cause of death in 1933 but is now almost eliminated. Diarrhea enteritis and pneumonia are responsible for high death rates among persons under five years of age. Tuberculosis, diseases of the heart, and cancer are responsible for high death rates among persons 25 years of age and over. Females have higher death rates from tuberculosis and cancer than males. Males have higher rates from diarrhea enteritis, diseases of the heart, and pneumonia than females. White people have higher death rates from diarrhea enteritis, pneumonia, and cancer than colored people. Colored people have higher death rates from tuberculosis and diseases of the heart than white people. Death rates from Diarrhea enteritis, tuberculosis, and pneumonia have declined in recent years, while the death rate from cancer has increased, and the death rate from diseases of the heart has remained about the same. The combined Spanish and United States culture systems are to a great extent responsible for the extreme case of population pressure that exists. The ADS Years of Spanish domination of the Island have left traditions and beliefs that still direct the way of thinking of most of the people. Many of these cultural traits have been affecting the Island’s basic problem, excessive population. Such things as unlimited reproduction, large families, and little emphasis on schooling are examples of the beliefs that tend toward the Island's high birth rate. On the other hand, the 50 years of American influence has provided the Island with modern ideas of sanitation, and public health programs that have made possible the reduction in the death rates from the different diseases, and as a result a higher life expectancy. Emphasis has been given to more schooling, small families, and limited reproduction, but the previous culture is still in the way. Although an attempt has been made to control the number of births, the results are nil. Besides, different historical periods have had their influence. During the depression years when there was food and money available through the different relief programs, the birth rates increased. The same thing happened during the World War II period when the birth rates were very high. On the contrary, the death rates have shown a decline every year, and in this phase the government has been successful. In view of what happens in countries where death rates have fallen more rapidly than birth rates, the future trend of population growth in Puerto Rico apparently will continue to increase. This means that population pressure will worsen unless cultural changes such as increased emphasis on schooling, industrialization, urbanization, and higher standards of living make the people more aware of the problem and cause them to change their present ideas and practices with respect to fertility. / Master of Science