Twelve parishes in Northumberland and County Durham were used to estimate the accuracy of Anglican marriage registers as indicators of migration between birthplace and marriage. We compared entries in the marriage registers with the annotated baptismal registers which exist for most Northumberland parishes from 1798-1812, and which explicitly document the birthplaces of the parents of the child baptised. By linking individual marriages and subsequent baptisms we showed that the marriage registers systematically underestimate the amount of migration, with values of f (predicted by Wright's Island model) estimated from marriage registers likely to be two to four times the size of those indicated by the baptism registers.