The present study investigated prospectively programmatic factors relating to dropouts in child vaccination in 6 subdistricts of Bangladesh. A cross-sectional survey (n = 2700) was conducted estimating overall coverage of immunization using cluster sampling. The eligible subsample of children (n = 1064) was followed up prospectively to understand reasons for dropouts. In-depth interviews (n = 73) with mothers/caregivers and service providers were done and EPI (Expanded Programme on Immunization) sessions were observed (n = 131). Irregular EPI sessions were the prime cause of dropouts particularly in low-performing subdistricts. The other programmatic factors linked with dropouts were (a) no reminder about subsequent session/doses, (b) unfriendly behavior or absence of vaccinator, ( c) refusal due to lost card or vaccine exhausted, and (d) short duration of sessions. Providers highlighted constraints such as financial problems for transportation, particularly in the hard-to-reach areas and vacancies of the posts of health assistants. The barriers to completing full schedules of vaccination can be removed to a large extent through programmatic adjustments.