Sequence data from a non-coding nuclear DNA segment (Cpnl-1) was used to investigate the divergence between Spanish and French subspecies of the grasshopper Chorthippus parallus which form a hybrid zone in the Pyrenees. The spatial distribution of eighteen Cpnl-1 sequence haplotypes from eighteen French and fifteen Spanish populations and phylogenetic analyses using both distance and parsimony procedures provide strong evidence that the Pyrenean hybrid zone was formed by postglacial secondary contact and that the French subspecies arose by range expansion from a Balkan or Italian refugium. In addition, the data provide evidence for subdivision between grasshoppers from Northern Spain and those from Central and Pyrenean Spanish populations.