In the Northern Health Region of Portugal, vaccine coverage is measured by checking and studying individual vaccination records in health centres. Each year from 2001-2004, birth cohorts completing 2, 6 and 14 years of age were selected for assessment. Data collection occurred on January the following year and meetings with district immunisation coordinators took place every March. For all vaccines and birth cohorts considered, vaccine coverage values observed in the north of Portugal were excellent. In this paper, we make comparisons with published international data on vaccine coverage and discuss validity issues; we believe that no serious biases have affected the validity of our vaccine coverage data but comparisons with international data must be addressed with caution; the methods we used have been useful in increasing vaccination coverage.