Background Although the majority of nations have routine immunization programs in place as a public health strategy, more than 1.5 million children under the age of 5 die yearly worldwide due to inadequate vaccination coverage. This study investigated the predictors of adherence to routine immunization schedules in Lira city. Methods This was a cross-sectional study among 420 caretakers of children aged 10 to 18 months. Bivariate and multiple regression analyses were conducted to assess the predictors of adherence to the full immunization schedule. A P-value > .05 was considered statistically significant at 95% CI. Results The study result indicated that the majority, 237 (56.4%) of caretakers were aged 25 to 34 years, 205 (48.8%) had attained primary level education, and 284 (67.6%) were married. The results showed that 365 (87.0%) had their children fully immunized. The predictors of adherence to full immunization schedule were knowledge on when to start vaccination (AOR:5.65; 95% CI:1.82-17.55; P = .003), maternal outcome expectations (AOR:3.45; 95% CI:1.16-10.29; P = .03) and maternal knowledge (AOR:2.15; 95% CI:1.18-3.90; P = .01). Conclusion The study findings show that 9 in 10 of the caregivers adhered to the immunization schedule. The significant predictors of adherence to full immunization were flexible clinical hours, maternal outcome expectations and maternal knowledge. Based on the conclusions we recommend that government and service providers be flexible in clinic hours and continue health education to women of childbearing age at an early stage, especially during antenatal care visits, delivery and the postnatal period on childhood vaccination to maintain adherence to the routine immunization schedule.