A total of 478 women wishing to use the Standard Days Method and meeting the eligibility criteria were admitted to the study after signing an informed consent form and interviewed monthly until they either completed 13 cycles of method use or left the study for other reasons. The first level of data collection was administered by the clients themselves. Each woman was asked to keep a daily diary to record menstrual bleeding, intercourse, and use of any other contraceptive method. The information on the diary card was reviewed by the clients and the service provider during each of the monthly follow-up contacts. In addition, follow-up forms were administered, which included questions concerning method use, satisfaction, and willingness to continue in the study.