OBJECTIVE: To evaluate the influence of aphasia on the cognitive screening test in stroke patients with unilateral cerebral hemispheric lesions. METHOD: We evaluated 51 hemiplegic patients with unilateral cerebral hemispheric lesions using CT or MRI. We divided the subjects into three groups according to the presence of aphasia and motor weakness: right hemiplegic patients with aphasia, right hemiplegic patients without aphasia, and left hemiplegic patients. Functional Independence Measure (FIM), Mini-Mental Status Examination (MMSE) and Neurobehavioral Cognitive Screening (NCSE) Tests were applied in all patients. RESULTS: No differences were observed in motor FIM scores between three groups. Total FIM and cognitive FIM scores of the right hemiplegic patients with aphasia were lower than those of the other two groups. MMSE and several sub-items of NCSE (orientation, attention, comprehension, repetition, naming and calculation) showed the same results. But the mean scores of memory, similarity, and judgement items in NCSE were higher in the left hemiplegic patients than the right hemiplegic patients. No differences were observed in the construction score. CONCLUSION: All three cognitive screening tests used in this study were remarkably influenced by the ability of the language function of the patients. Lack of adequate items to detect right cerebral hemispheric lesions were also noticed.