The purpose of this study was to identify the existence of Relative Age Effect (RAE) at youth level in both elite and amateur Spanish soccer clubs, and also to carry out an analysis providing with information on how this effect has evolved in recent years. We have obtained information on the youth teams of the 20 clubs belonging to the Spanish Professional Football League (LFP) in two separate seasons (2005-2006 and 2008-2009) as well as data on five youth academies belonging to amateur clubs. The collected data revealed an over- representation of players born in the first months of the selection year in all groups of analysis (Elite 2005-2006, Elite 2008-2009 and Amateurs), although only the Elite groups showed significant variations in birth-date distribution in relation to the Spanish population. The results showed a reduction in RAE from the 2005-2006 season to the 2008-2009 season. The following variables - playing position, the number of years each player has spent in their specific age group and the category of the team at each club were shown not to have influence on the extent of RAE.

• There was RAE in all groups analyzed, although only the Elite groups showed significant variations in birth-date distribution in relation to the general population.

• RAE is more evident in the Elite groups than in the Amateur probably because of the detection process, which is more thorough in the Elite groups.

• Playing position, number of years in their specific age group and category of the team did not have any influence on the extent of RAE.

• Any attempts to prevent RAE should be based on a stable sport policy and the implication of all the stakeholders in the system. All of them should think in the development of a player as a long-term project.