OBJECTIVE: There is little information about vaccine schedule compliance in very-low-birth-weight infants in developing countries. The aim of the study was to describe the compliance with the vaccine schedule among this population in Lima, Peru. PATIENTS AND METHODS: We conducted a prospective cohort study in four hospitals in Lima in infants with a birth-weight of less than 1500 g, followed from birth up to 12 months of age every 2 weeks. The date and age at administration of each vaccine was recorded RESULTS: 222 infants were enrolled. The median birth-weight was 1250 g (range 550-1499 g) and the median gestational age was 30.0 weeks (range 23-37 weeks). The mean age for the first pentavalent (DPT, Hib, HepB) and oral polio vaccine administration was 4.3 +/- 1.4 months in infants with a birth-weight of < 1000 g vs. 3.1 +/- 1.0 in infants with a birth-weight 1000-1500 g (p < 0.001); 4.1 +/- 0.9 vs. 3.3 +/- 1.1 for rotavirus (p < 0.05); and 5.1 +/- 2.1 vs. 4.3 +/- 1.8 for the 7-valent pneumococcal conjugated vaccine. Only 35% had received the three doses of oral polio and pentavalent vaccine by seven months, although by nine months 81% had received these vaccines. CONCLUSIONS: Vaccination of very-low-birth-weight infants in Peru is significantly delayed, especially in infants with a birth-weight of < 1000 g and lower gestational age. Urgent educational interventions targeting physicians and nurses should be implemented in order to improve vaccination rates and timing in these high risk populations.