Introduction: The main concern about increase in the world's population is the threat of millions of human lives, the majority of whom are women and children. Still 25–50% of the last pregnancies in developing countries are unwanted. The aim of birth control is to decrease unwanted pregnancies and ultimately improving physical and emotional health of women and even children. Sterilization (tubal ligation in women or vasectomy in men) is one of the most reliable contraceptive methods. Various studies have referred to age, marriage age, number of children and religions beliefs as the related factors for selection of sterilization as a contraceptive method. Asian and African studies demonstrate that couples who choose sterilization as a contraceptive method have a positive attitude and those who do not choose it have a negative or neutral attitude toward sterilization. However, knowledge of both groups about sterility is mostly poor. This project aims to identify and compare knowledge, attitude and the related factors which involve with choosing sterilization as a contraceptive method in users of sterilization method and in users of other contraceptive methods, in Hamedan city in 2003. Materials and methods: The descriptive study was performed on 130 couples, including 65 couples who chose sterilization and 65 couples who chose other contraceptive methods, with at least 3 live children. All couples had either referred to Hamedan's hospitals (for sterilization) or to health care centers (to get contraceptives). Information characteristics such as, age, education, race, address, career, number of children, duration of marriage, age of last child, discrepancy between number of children and the desired number of children, reasons for choosing the contraceptive method, related knowledge and attitude, were recorded in the questioner. Statistical methods include chi-square, analysis of variance, correlation coefficient, t-test, Fisher and Kroscal Valis were used. Results: Among the couples, who selected sterilization, 52.3% had a poor knowledge and 78.5% had a positive attitude. Thirty percent of subjects were aware of the rate of reversibility of fertility and 17.5% were aware of the duration of contraception use after vasectomy. Among the eligible couples for sterilization who were using other contraceptive methods, 50.8% had a weak knowledge and 49.3% had neutral attitude. Twenty percent of couples were aware of the rate of reversibility of fertility following sterilization and 13.8% were aware of the duration of using a contraceptive method after vasectomy. There was no significant difference between knowledge of two groups while there was a significant difference between their attitudes (p < 0.01). The source of information in 27.7% of women who chose sterilization was the health care centers and that of 16.9% of such men were relatives and friends. Conclusion: Couples with poor knowledge and positive attitude tend to choose sterilization and those who have a neutral attitude do not select it. Education and counseling are highly recommended for both selecting and not selecting sterilization as a contraceptive method.