A field trial to assess the effectiveness of a reminder sticker in reducing immunization dropout rates was conducted in two districts of Addis Ababa between October 14, 1991 and January 31, 1992. A total of 703 children were entered into the study. The study population was divided into intervention and control groups according to a randomly determined schedule. The intervention group received the reminder sticker and the control group did not recei ve the sticker. All other services were identical. A baseline interview documented the socio-demographic and maternal characteristics potentially related to immunization services utilization and revealed no statistically significant differences between the intervention and the control group. The dropout rates were 7.3% and 13.3% in the intervention and control groups respectively. The Relative Risk of being a dropout in the intervention group was 0.55(0.35,0.87) . This difference is clinically and statistically (p<.Ol) significant. Therefore, it is concluded that the reminder sticker is effective in reducing immunization dropout rates. Further, large scale investigations under operational conditions are recommended prior to the routine introduction of stickers into the immunization services