Continuation rates in program participation and use of contraceptive methods were studied in the family planning program conducted by the Secretaria de Salubridad y Asistencia (Department of Health and Welfare) of Mexico. The rates were found to be comparable to those prevailing in other developing countries, but the dropout rate was sufficiently high to weaken the impact of the program on health conditions and birthrate. The findings are summarized in 12 tables. The principal cause of discontinuation identified in the study is a widespread ambivalent attitude toward the program among participants, which causes them to resent difficulties in obtaining services and using contraceptive methods. The principal difficulties to which participants respond by abandoning the program are: the method provided under the program (continuation rates were considerably higher with IUDs than with oral contraceptives), lack of adequate information about the program and the methods offered, and relatively long waiting time at family planning centers. Alemán