Abstract. Background: The science of demography is very new in Iran, as its introduction to Iran and the start of demographic investigations goes back to half a century ago. Because of its importance and effects, it seems now, that the time is ripe that special attention should be paid for the capacities of this science in medium and long term planning and decision making. Fertility is one of the essential subjects dealt by demography, as the survival and continuation of the population have their roots in it. The importance of fertility for demographer is to that extent that they consider it as one of the four vital events and since it directly affects the increase and decrease of population, therefore, fertility is regarded the important factor in population changes. The purpose of the present research is to examine undesirable consequences of uncontrolled fertilities and their negative effects on the economic growth of Iran. A study of Iranian age pyramid of population explicitly indicates that the trend of fertility is entangled in a state of disequilibrium and unplanned for years, so that, during 1977-87 years, child bearing had its highest record in the history of the population of Iran, which caused an average rate of 3.9 percent yearly growth. The most important outcome was an increase in age group of 0-4 years in these years. After this period, the economic and social crisis in one hand and governments awareness of family planning on the other hand, caused a decline in the fertility trend. This ultimately created an inflationary age group continuously ascending in the age pyramid. Materials and Methods: Data related to this research are on the basis of the information and statistics presented by Statistical Center of Iran and study and analysis of the censuses carried out in Iran. Result: According to the last census carried out in the year 2006 in Iran, the largest age groups of population are those of 15-19 and 20-24 years old, which indicates an adolescence population. Although this may be considered as a promising phenomenon which conform foundations for development in Iran, it may also create difficulties' in the process of the development of Iran, in the absence of favorable grounds for development. Another important point is the movement of population inflation higher up to older age groups. In the other word, Iran is rapidly progressing towards population ageing. Appropriate laws and proper planning is needed in this respect. Conclusion: In this essay, effort is made to avoid any prejudgments. Firstly, the past present and future of the fertility and population in Iran are studied. Then, consequences of the uncontrolled fertilities on the economic growth of Iran are examined. Population forecast show that population of Iran will be a very aged population in 32 years from now. The process of economic growth in Iran is confronting concerns and difficulties due to above mentioned population changes in the past, present and future. This is much worrying when it is seen that there is no any special planning by governments to benefit and use capabilities and capacities of the population in the process of growth.