OBJECTIVE: To determine what contribution the Standard Days Method® (SDM) makes to the contraceptive mix offered by regular health services in areas of Peru where contraceptive prevalence rates (CPR) are already high. METHODS: SDM was added to the family planning methods offered by the Ministry of Health in two provinces in Peru in September 2002. Retrospective interviews were conducted in March-June 2004 with 1 200 women who had chosen SDM as their contraceptive method and had used it for 2-20 months. Data were also obtained from the databases of the participating health services. The evaluation covered SDM demand, whether or not clients were switching to SDM from other modern methods, and SDM continuation and effectiveness. RESULTS: Demand for SDM stabilized at 6% of all new family planning users. Most users had not been using any reliable contraception at the time they started using SDM. About 89% of those who began using SDM at least 6 months before the interview were still using it at 6 months. The 12-month typical use pregnancy rate was estimated to be around 10.0 per 100 women years. CONCLUSIONS: Adding SDM to a program's existing contraceptive method mix can increase coverage even in an already high-CPR setting. Most women who choose SDM do not switch from any other modern family planning method. Continuation compares well with other modern user-directed methods. SDM effectiveness, when offered in regular service delivery circumstances, compares well to efficacy trial findings.