A levonorgestrel-releasing IUD and the Copper T 380Ag IUD were in randomized comparison for seven years in five clinics. In two other clinics the randomized study was truncated at five years, but use of the Copper T continued. No pregnancies occurred to users of either device in years 6 and 7. Cumulative pregnancy rates were 1.1 per 100 at seven years for the steroid-releasing and 1.4 per 100 for the copper-releasing IUDs. Cumulative rates of PID did not differ between devices. Infection rates appeared to be lowest during the sixth and seventh years of the study. Termination attributable to amenorrhea was the principal contributor to differences in cumulative continuation rates between devices. At the five clinics that carried the comparative study to seven years, cumulative continuation rates were 24.9 per 100 for LNg20 IUD users and 29.4 per 100 for TCu 380Ag users. Women who used either method for periods of five to seven years experienced, on average, marked to mild increases in hemoglobin as compared with levels at admission. The Copper T380 family and the LNg20 IUDs represent the most effective reversible contraceptive methods yet studied in long-term randomized trials.