The GABAergic neurons of the thalamic reticular nucleus (TRN) play a critical role in the generation and control of spike-and-wave discharges (SWDs) in absence epilepsy. We have used the disector method to count the GABA+ve and GABA-ve neurons in the intermediate TRN sector of genetic absence epilepsy rats from Strasbourg (GAERS) and of Wistar rats during postnatal (P) development at P10, P20, P30, and P60 days. The same part of TRN was removed from each animal, the GABAergic neurons were labelled using light-microscopical GABA immunohistochemistry and the data were statistically analysed. Both the GAERS and Wistar animals showed an increase in the density of GABA+ve and GABA-ve cells from P10 to P20. From P20 to P60, Wistar animals showed no significant differences for either cell type, but in the GAERS a progressive decrease from P20 to P60 was observed in both GABA+ve and GABA-ve cells. The decrease of the GABA-ve cells was more pronounced than that of the GABA+ve cells. There were no significant differences between cell sizes for GAERS and Wistar rats at any developmental age. The lower density GABA+ve and GABA-ve neurons at P30 and P60 of GAERS compared to Wistar animals may contribute to the generation of SWDs in absence epilepsy.