This study investigates the linguistic abilities of individuals included in the so-called Autism Spectrum Disorder (ASD) and the language difficulties observed in this cases. The analysis of language problems in autism, with data from Brazilian Portuguese (BP), from a perspective that articulates Linguistic Theory, in its minimalist assumptions, with the psycholinguistic research, motivated this research. The purpose of this study was to evaluate the linguistic abilities of BPspeakers in the autistic spectrum in order to verify the extent to which high costly structures cause them processing difficulties and, in particular, if their language difficulties can be related to problems in the Grammar-Pragmatics interface. A preliminary study was conducted with a adolescents diagnosed with ASD between 16 and 21 years of age, with varied degrees of intellectual development and communication skills and a age-matched group of ASD individual, homogeneous, with regard to degrees of intellectual development and communication skills Module 1 of MABILIN (Modules of Evaluation of Linguistic Abilities), developed in the Laboratory of Psycholinguistics and Acquisition of Language (LAPAL/PUCRio). It is a battery of picture-identication tasks for the assessment of the comprehension of highly costly structures: passives, relatives and WH/WH+N interrogatives. The results obtained indicate below-average performance in the first group in the most demanding sentences, such as reversible passives, object relative and WH+N questions, though lower cost structures, such as subject relative clauses, also presented difficulties for them. The performance of the second ASD group was compatible with typical development. The investigation continued with 7-13 year old autistic children with high degree of intellectual development and communication skills and an age-matched group of typically development children (TD). The scores of the ASD group were below those of the TD children in MABILIN 1, though the results were not indicative of syntactic impairment. Five experiments were conducte with these groups of children making use of pictureidentication tasks and an interactive task, in which Theory of Mind was alsoevaluated. The expreiments focused on children s knowledge/access to formal features of functional categories at the grammar-pragmatics interace: aspect, mood, definiteness. Ambiguity in pronominal reference and the comprehension of reflexives and accusative pronominals were also investigated. The ASD group showed lower scores than the TD group in all tasks taken together. These groups differed particularly in the comprehension of mood, reflexives and accusative pronominals.