The Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) is an individually administered clinical instrument designed for assessment of intellectual abilities of adolescents and adults. The WAIS-IV consists of 15 subtests (10 core and 5 supplemental) reflecting the efficacy of cognitive functioning in four domains (verbal comprehension-VCI, perceptual reasoning-PRI, working memory-WMI, and processing speed-PSI), and general intellectual ability (Full-Scale IQ-FSIQ). The WAIS-IV was administered to a sample of 262 respondents – specifically, 104 respondents from sample representative for the wider Belgrade area, 62 schizophrenic, 63 depressive, and 33 patients with intellectual disability. Psychometric properties of WAIS-IV subtests were analysed within the frameworks Item Response Theory (IRT) and Classical TestTheory (CTT). Results show that IRT reliability of subtests ranges from .86 (Comprehension and Picture Completion) to .95 (Cancellation), while the IRT reliability of the FSIQ is .94. Overall, all subtests discriminate participants well along the whole continuum of intellectual abilities. The WAIS-IV enables highly reliable assessment of intellectual abilities on Serbian population.