Vasectomy is greatly underutilized in most countries in part because it is the least promoted of all modern contraceptive techniques. If providers have favorable attitudes toward vasectomy a good understanding of the decision making process that leads to vasectomy enhances their ability to encourage the use of this method. Furthermore thorough counseling of vasectomy seekers will significantly increase acceptance. The purpose of this article is to define the decision making process and to discuss how this information can be used in family planning programs. An in-depth study was made of the decision making processes of 235 couples using the counseling services of the Planned Parenthood Association of Houston Texas in order to understand the decision making process. The process took from 2 to more than 10 years and has the following events in common: became aware of vasectomy; talked to a vasectomized man; decided to have no more children; decided temporary contraceptives were no longer acceptable; decided vasectomy was the best contraceptive method; had a scare (a missed period or severe side effects from the pill). Information gathering by acceptors occurred throughout the process with men faltering on the way toward vasectomy because they lacked information from an influential source not because they had been exposed to a casual dose of misinformation. Sources questioned include physicians (usually gave incomplete answers); reading material (less than 50% used this source); vasectomized men (9 out of 10 used this source and felt it to be most influential). Questions most men ask are listed in the article. Guidelines for counselling are suggested. Specific suggestions for program administrators are offered based on the 5 phases most men pass through before getting a vasectomy. Phase 5 when a decision is made is the best time for an information and education program through the mass media. Other stages suggest capitalizing on the presence of vasectomized men in their communities and in-depth media campaigns. (authors modified)