Hypoxia, reduced cerebral perfusion and sleep fragmentation as the result of recurrent apnea-related episodes in sleep apnea patients may have impact on mental performance such as memory and concentration. Increased number of traffic accidents has been observed in OSAS patients. Patients often complain of concentration and memory problems, as well as sleepiness. The diagnosis of perception processes requires neuropsychological diagnosis. 22 sleep apnea patients were involved in the study. Correlation between the number of mistakes in Benton Test and AHI has been observed (r = 0.63; p < 0.005), as well as between AHI and memory in Number Repeating Test based on Wechsler-R (r = 0.49; p < 0.05). No correlations have been found between results of Benton Test and sleepiness scale. Mean saturation and lowest saturation didn't show any correlation with neuropsychological tests. Qualitative analysis of mistakes in both Benton and Bender-Gestalt Tests did not suggest any organic changes in the brain. AHI seems to be more important predictor of memory dysfunction than sleepiness scale score. Specific tests, specially used in neuropsychological diagnosis, could be useful in the diagnosis of memory perception disorders and treatment effectiveness assessment in OSAS patients.