There are few data, especially outside the United States, examining the timeliness of childhood vaccination, although it is of key importance for diseases such as pertussis, and invasive disease due to Haemophilus influenzae type b and Streptococcus pneumoniae. The aim of this study was to use the unique resource of the Australian Childhood Immunisation Register (ACIR) to examine trends in and factors associated with timeliness of infant vaccination at the national level. As in previous studies, age-appropriate immunisation was defined as within 30 days of the recommended age. Vaccination delays became more common for later doses, given at an older age, but long delay (greater than 6 months) occurred in only 1-2%. Although immunisation coverage increased over time, timeliness did not improve. Among Indigenous infants, long delays occurred in 5-12% of those residing in very remote areas, but by 2 years of age, overall immunisation coverage was similar to non-Indigenous children. With immunisation coverage at the key indicator ages of 12 and 24 months now high in most industrialised countries including Australia, timeliness of vaccine doses should be the next benchmark to aim for in program performance, especially in specific sub-groups such as Indigenous children who stand to gain most from prevention of early onset disease.