The Wechsler Adult Intelligence Scale, fourth version (WAIS-IV), is a frequently used instrument for neuropsychological assessment. The aim was to assess the degree of conformity between the Scandinavian adaptation of the WAIS-IV and a short form of this scale (SF) in a mixed sample of neurological diagnoses. The SF comprised Block Design, Similarities, Digit Span, Arithmetic, Information, Digit Symbol (in the WAIS-IV named Coding), and Picture Completion, the latter here replaced by Matrix Reasoning. The sample consisted of 150 patients and included multiple sclerosis (n = 27), brain tumor (n = 15), traumatic brain injury (n = 60) and vascular brain damage (n = 48). There was a lack of congruence between the WAIS-IV and the SF in the entire sample, revealing selectively significantly higher scores for the SF on Full Scale IQ (FSIQ) and Processing Speed Index (PSI). On a diagnostic group level, the discrepancies were as follows: in the traumatic brain injury group on FSIQ, Verbal Comprehension Index (VCI) and PSI, in the vascular damage group the FSIQ was significantly higher on SF compared to the WAIS-IV. Since the results revealed several mismatches between the SF and the WAIS-IV, except for the MS and traumatic brain tumor group, there is a lack of interchangeability between these two sets of tests. Thus, generally the SF cannot be recommended as a substitute for the WAIS-IV in this type of mixed Swedish neurological sample. The small sample sizes make the generalizability of this study limited.