OBJECTIVE To study the effectiveness of planning and management interventions for ensuring children in India are immunized at the appropriate age. METHODS The study involved children aged less than 18 months recruited from Haryana, India, in 2005-2006: 4336 in a pre-intervention cohort and 5213 in a post-intervention cohort. In addition, immunization of 814 hospitalized children from outside the study area was also assessed. Operational barriers to age-appropriate immunization with diphtheria, pertussis and tetanus (DPT) vaccine were investigated by monitoring vaccination coverage, observing immunization sessions and interviewing parents and health-care providers. An intervention package was developed, with community volunteers playing a pivotal role. Its effectiveness was assessed by monitoring the ages at which the three DPT doses were administered. RESULTS The main reasons for delayed immunization were staff shortages, non-adherence to plans and vaccine being out of stock. In the post-intervention cohort, 70% received a third DPT dose before the age of 6 months, significantly more than in the pre-intervention cohort (62%; P = 0.002). In addition, the mean age at which the first, second and third DPT doses were administered decreased by 17, 21 and 34 days, respectively, in the study area over a period of 18 months (P for trend < 0.0001). No change was observed in hospitalized children from outside the study area. CONCLUSIONS An intervention package involving community volunteers significantly improved age-appropriate DPT immunization in India. The Indian Government's intention to recruit village-based volunteers as part of a health sector reform aimed at decentralizing administration could help increase timely immunization.