The study analyzes the records of 833 persons who received North Atlantic Treaty Organization (NATO) Postdoctoral Fellowships from 1959 through 1981. To assess the program's long-term effects, the study focuses on information about the current career status of fellowship recipients and compares them with two similar groups: National Science Foundation Postdoctoral Fellows from the same period, and persons to whom the NATO Fellowship was offered but who declined it. Following a description of the programs and the study methodology, results are reported in the areas of: personal characteristics, involvement in prior NSF programs, degree institutions, fields of science, institutions chosen by NATO Fellows, employment of NATO Fellows after tenure, current employment, reasons for NATO Awardees declining the Fellowship, research support following the Fellowship, tenure-track progression, prizes, and memberships in national academies. The study found that all three groups experienced roughly equivalent success in obtaining later research support and employment at research universities. Biological scientists were the leading recipients of both NATO and NSF postdoctoral awards, followed by chemists and physicists. Appendices examine multiple awardees and characteristics of NATO and NSF Postdoctoral Fellowship Awardees. (JDD)