This article aims to outline the areas of investigation useful for the clinical evaluation of specific language impairment (SLI) and learning disabilities (LD) in the condition of bilingualism, especially in children who learn Italian as a second language (L2). This is an extremely heterogeneous population in terms of clinical phenotypes, environmental factors and timing of exposure. We focus in particular on the type of bilingualism that is defined subtractive, in which the social value of the mother tongue (L1) is not recognized. Starting from the diagnostic approach of neurodevelopmental disorders in which phenotypic variables intersect with environmental variables in a temporal continuum, we try to apply the same approach to bilingual children. We outline the most important steps of anamnesis and clinical evaluation in both SLI and LD, and the principal environmental and temporal elements that must be taken into consideration.