In 1996, four provinces of Iran experienced below replacement level fertility. Since the early 1980s, these provinces have recorded lower fertility than the national level. How and under what condition has fertility declined to such a low level in these provinces? It may be of considerable interest to examine whether these provinces can be regarded as the leaders of the fertility transition in Iran. What are the likely effects of below-replacement fertility on population growth in Iran in the short term? Will Iran, as a whole, experience below replacement fertility in the near future? What would be the reaction of the government if below-replacement level fertility is reached in the near future? This paper will first, assess and analyse the fertility trends in the provinces of Isfahan, Gilan, Semnan and Tehran as compared with the national level during the period 1972-1996. Using available data, an attempt will also be made to estimate recent fertility levels for these provinces. Second, demographic and socio-economic characteristics, as well as contraceptive use, in these provinces will be reviewed; female singulate mean age at marriage and age-specific proportions married for 1976, 1986 and 1996 will then be examined. Third, the prospects of low fertility in Iran as well as the likely reaction of the government on low fertility will be discussed thereafter.