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 14 October 1991 and 31 January 1992. A total of 703 children were entered into the study. The study population was randomly divided into intervention and control groups. The intervention group received a reminder sticker and the control group did not. 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 two groups. The dropout rates were 7.3 and 13.3% in the intervention and control groups respectively. This difference is clinically and statistically (P < 0.01) significant. Therefore, it is concluded that the reminder sticker is effective in reducing immunization dropout rates. Further investigations under operational conditions are recommended prior to the routine introduction of stickers into the immunization services.