The literature on political parties has highlighted the influence of intraparty factors such as the origins (particularly, the modes of party formation) or the ideology on the process of institutionalization (e.g. Panebianco, 1989; Bolleyer 2013).  However, the impact of external factors has not been properly explored. This paper will use the comparison between two Spanish case studies to point out the relevance of the regional level in the process of institutionalization of two brand new Spanish parties such as Podemos and Ciudadanos. Despite their different ideology, origins and popularity, by early 2015 both parties were leaded by cohesive, young and popular leaderships that hardly had the opportunity to expand their organizations at any Spanish region (e.g. Rodríguez-Teruel and Barrio 2015, Rodríguez-Teruel et. alt, 2016). Hence, the paper will examine first the different strategies conceived by the two parties to expand their organizations at the regional level. Then, it will consider what were the main impacts of each strategy on the ongoing process of institutionalization of each party. So far the academy has pointed out that both strategies indeed affected their voters (e.g. Fernández Albertos, 2015; Rodríguez-Teruel, et. alt. 2016), but little attention has been paid to the organizational dimension. Building on new conceptualizations of party institutionalization (e.g. Arter and Kestilä-Kekkonen, 2014; Casal-Bertoa 2016; Harmel, Svasand and Mjelde 2016), the paper will mainly focus on this internal dimension of the institutionalization and assess the relevance of these evidences for the comparative literature.