This article attempts to explain the impact of department-level political opportunity structures on the electoral success of the French Front National (FN) in the 2004 regional elections. The concept of 'political opportunity structure' refers to the degree of openness of a particular political system and the external institutional or socio-economic constraints and opportunities that it sets for political parties. Comparative analysis across subnational units is conducted where the 94 departments of mainland France are the units of analysis. The significance of electoral institutions (district magnitude), party competition (effective number of parties), electoral behaviour (turnout) and socioeconomic conditions (immigration and unemployment) on the ability of the FN to gather votes across the departments is assessed by means of multiple regression. The empirical results show that the subnational political opportunity structures have been of great importance for the FN. Some four out of the five independent variables are statistically significant and explain a great deal of the variance in the two dependent variables (electoral support for FN list and index of electoral success). Turnout and district magnitude are negatively correlated with the electoral fortunes of the FN, while unemployment and the effective number of party lists are positively correlated with the success of the FN in the regional elections. The variable that indicates the share of non-European immigrants does not provide additional explanatory power in a statistically significant way.