This systematic literature review explored the state of the art concerning the theoretical and empirical knowledge of the twice-exceptionality of Intellectual Giftedness and Autism Spectrum Disorders (IG + ASD), in relation to diagnostic and assessment issues. After searching and examining publications in peer-reviewed journals and dissertations, we encountered a variety of methodologies being used. The results showed the absence, until now, of theoretical conceptualisations of the phenomenon IG + ASD. Nevertheless, this contribution revealed some converging tendencies concerning both personal characteristics and diagnostic and assessment issues, between publications with and without Systematic Identification Measures (SIM). Some findings, like the "superior non-verbal abilities", are discussed in relation to (controversial) image formation of IG and IG + ASD. Altogether, the results indicated the need for an in-depth exploration and conceptualisation of the phenomenon IG + ASD. Meanwhile, future research should also address the practical psychological-educational need for both classification-based and needs-based assessment procedures, regarding students with (suspicion of) IG + ASD. (Contains 4 tables.)