In Ultra High Risk (UHR) studies, intellectual functioning is commonly assessed using premorbid IQ tools as a covariate. The aim of this study was to show that the use of the Wechsler Adult Intelligence Scale (WAIS) could yield accurate neuropsychological profiling and that an alternative approach such as a multiple-case study could be a more interesting way to isolate discrete cognitive processes in the early stage of illness. The studied population consisted of 198 adolescents and young adults (16–30 y.o.) referred to our outpatient clinic. After the CAARMS' interview, we defined 3 subgroups: UHR (N = 104), First Episode (FE; N = 30), and Help-Seekers (HS; N = 64) who were neither UHR nor psychotic. Intellectual functioning was assessed by the WAIS-III (9 subtests version) and ‘heterogeneous’ intellectual profiles were defined based on the existence of a 3-point difference in scoring at subtests constitutive of the same WAIS index. While UHR did not differ from FE or HS on WAIS' scores and sub-scores, the multiple-case study indicated a higher proportion of ‘heterogeneous’ profiles in the Verbal Comprehension Index in the UHR sample than in FE and HS (p = 0.04). The disease progression could heterogeneously impact on specific domains, in patterns depending on the stage of the illness. This approach exploring intra-subject WAIS performances might be more relevant than the use of global scores in detecting the subtle cognitive alteration of emerging psychosis.