During the past three decades the urban population of the developing countries has increaset1 tremendously. Most of this urban population growth has taken place on the metropolitan fringe, Also, about 42 cent of the developing countries urban population live in informal settlements, many located on the urban fringe.The demographic processes in the Tehran Metropolitan Region (TMR) during the past three decades reveals that while the population of the Tehran city has grown only 2, 3 times, the population of the rest of the TMR has grown by 7.8 times during the said period. Also, during the twenty-year period between 1976-1996 about 40 per cent of the five million-population increase of the TMR, have resided in informal settlements.The unprecedented growth of informal settlements in the TMR, has brought about many socio-economic, cultural environmental and political problems. This article which is based on the findings of a research project funded by the Tehran University, attempts to survey some socio-economic characterics of the households residing in some of the spontaneous settlements on the Tehran Metropolitan Fringe, specifically trying to answer the following questions:1. Are these settlements functionally integrated with rural areas or with the Tehran Metropolis?2. Are the residents of these settlements engaged in the formal or informal economic act ivies?This is done by surveying 206 households (selected by random sampling techniques) in three spontaneous settlements, namely, Bagher Abad, Saleh Abad, and Khtoon Abad, located in the vicinity of Tehran's three major transportation routes.The findings of the study reveal that; the spontaneous settlements studied are not functionally integrated with rural areas, but rather with the Tehran Metropolis: and that many fringe workers are informally employed.