The present socio-cultural situation in the Basque speaking area of Spain offers a privileged field for the study of Spanish loanwords in Basque, due to the more expanded use of Basque, together with a better knowledge of Spanish among Basque speakers. Within the theoretical framework of Natural Phonology, this paper explores some phonological and lato sensu morphological mechanisms that take part in the integration of Spanish loanwords into Basque. First it deals with the mutual influence between Spanish and Basque when both are first languages for the speaker. Early bilingualism only causes the loss of Basque processes that are suppressed in Spanish, but those processes need not be completely lost. There is clear evidence that continued collective bilingualism and need of translation motivate the transformation of denaturalised phonological substitutions into morphological devices for the adaptation of loanwords.