Primary objective: To assess the criterion and construct validity and inter-rater reliability of the Czech version of the Mississippi Aphasia Screening Test (MASTcz). Research design: Prospective evaluation of consecutive inpatients admitted to the stroke unit of a university hospital within 60 days of onset of a unilateral left hemispheric ischaemic or haemorrhagic stroke with documented aphasia (LHA + ; n= 149). As control groups, unilateral right hemisphere stroke patients without aphasia (RHA−; n= 45) and healthy volunteers recruited from the community to comprise a non-patient control group (CG; n= 243) were examined. Methods: Data collection included administration of MASTcz (in 52 LHA + patients, repeated by two blinded observers within 24 hours), Edinburgh inventory, Minimental State Examination score and chart review. The presence of aphasia was documented with a standard clinical logopaedic examination and also with the Western Aphasia Battery (WAB) in 45 LHA+ patients. Results: MASTcz displayed high criterion validity (with sensitivity and specificity above 90%) in discrimination between stroke aphasia patients and both control subjects and RHA− stroke patients, high construct validity (close correlation with WAB score; r= 0.933), and acceptable interrater reliability. Conclusion: Analyses suggest the usefulness of MASTcz as a reliable and valid screening tool for the detection of aphasia and tracking of its progress.