Progestogen-only oral contraceptives (POCs) are generally considered a good contraceptive choice for brestfeeding women and for women who want to use an oral form of contraception, but are not suited for, or cannot tolerate the side effects of, estrogen-containing preparations. However, a number of POCs' safety, efficacy and other related issues remain to be addressed. This paper reviews recent literature and evaluates these issues from an epidemiologic perspective. The small number of users imposes severe limitations in designing epidemiologic studies to address POCs' long-term safety issues, but available information suggests POCs are at least as safe as, if not safer than, COCs. Compared to COCs, POCs are more likely to cause menstrual disturbances which, in turn, could affect their acceptability and lead to poor compliance and hence higher pregnancy rates. POCs' efficacy has been estimated to be between 1.4 and 4.3 pregnancies per 100 woman-years of use. Lower pregnancy rates approaching those of COCs have been reported in centers with good counseling. POCs' benefits outweigh their risks. However, more studies are needed to further address POCs' safety and efficacy issues.