Background: Non-adherence to treatment in seniors with dementia is a frequent and potentially dangerous phenomenon in routine clinical practice which might lead to the inappropriate treatment of a patient, including the risk of intoxication. There might be different causes of non-adherence in patients with dementia: memory impairment, sensory disturbances, limitations in mobility, economical reasons limiting access to health care and medication. Non-adherence leads to serious clinical consequences as well as being a challenge for public health. Aim: to estimate prevalence of non-adherence in seniors with dementia and to study correlation between cognitive decline and non-adherence. Subjects and Methods: Prospective study, analyzing medical records of seniors with dementia admitted to the inpatient psychogeriatric ward in the Kromeriz mental hospital from January 2010 to January 2011. Cognitive decline measured by MMSE, prevalence of Non-adherence to treatment and reasons for patient Non-adherence were studied. Results: Non-adherence to any treatment was detected in 31.3% of seniors; memory impairment was the most common cause of non-adherence to treatment. Conclusion: In conclusion, non-adherence to treatment in the studied group of seniors with dementia correlates with the severity of cognitive impairment – a higher cognitive decline correlates with a higher risk of non-adherence to treatment. and J. Lužný, K. Ivanová, L. Juríčková