ObjectiveTo assess physicians' knowledge and practices of modern methods of natural family planning.MethodsA questionnaire was mailed to 840 physicians selected randomly from Missouri state licensing records for obstetrics-gynecology, family practice, general practice, and general internal medicine.ResultsThe response rate was 65%. A total of 375 physicians (69% of respondents) saw women for reproductive issues. About half (46%) of physicians reported that they mentioned natural family planning to at least some women when discussing family planning issues. Observing vaginal discharge of cervical mucus was discussed by 40% of physicians in the context of avoiding pregnancy and by 36% of physicians in the context of helping a couple achieve pregnancy. Twenty-two percent of physicians estimated the best possible effectiveness of natural family planning to avoid pregnancy to be greater than 90%, and 35% estimated the actual effectiveness to avoid pregnancy to be greater than 70%. (The threshold rates of 90% best possible effectiveness and 70% actual effectiveness were chosen to be somewhat less than those reported in medical literature.) Physicians who gave higher estimates of effectiveness of natural family planning and physicians who were aware of an instructor in their community were more likely to provide women with relevant information about natural family planning.ConclusionMost physicians, especially those unaware of availability of instructors in their areas, underestimate the effectiveness of natural family planning and do not give information about modern methods to women