This paper analyses the border effect in Spain using a unique dataset on intranational trade flows over the period 1995-98. The results indicate that, after controlling for market size and distance, Spanish regions trade around 22 times more with the rest of Spain than they do with OECD countries. Moreover, the size of the Spanish bias is lower in the case of the Spanish regions'exports than in the case of imports, although the difference is not statistically significant in most cases. Finally, the border effect is not uniform across Spanish regions. © Blackwell Publishing Ltd 2005.