The purpose of this research is to analyse the evolution of fertility behaviour in Belgium through the 20th century from a longitudinal perspective, and to test the hypothesis of a spatial convergence during this period. It is based on the 1981 and 2001 censuses data. Firstly, we verified data quality and tested for recall bias and selection effects, which are often observed in retrospective data. Our tests show that such biases are not significant. Secondly, we used cluster analysis to create a typology of the evolution of fertility behaviour through the 20th century at the municipality level. The six clusters obtained present distinctive profiles and a great spatial coherence. The analysis of these six types of fertility evolution points to a certain spatial homogenisation of demographic behaviours, which reaches its maximum in the 1940’s generations. However, for the following generations, the disparities between municipalities types increase again.