Background and aims: Alzheimer is one of the most common diseases in adults with Down syndrome. This disease is associated with several behavioral problems & psychological states. The present study aimed to compare the behavioral and psychological symptoms of adults with Down syndrome in two groups of subjects with and without Alzheimer’s disease.

Methods: The research method was causal-comparative and the study population was all of adults with Down syndrome which held in the centers of handicap & intellectual disability of Tehran city in 1394 on a full-time basis or engaged in the rehabilitative activities on a part-time basis. Using the convenient sampling, 35 people without Alzheimer’s disease and 24 people with Alzheimer’s disease were selected and compared. The material was Dementia Screening Questionnaire for Individuals with Intellectual Disabilities which developed by Shoumitro in 2007. Collected data were analyzed through statistics such as mean, standard deviation and multivariate analyze of variance.

Results: In general, the results indicated a significant difference between the two groups in terms of the behavioral and psychological symptoms as well as subscales such as hostility/aggression, destruction of property, noncompliance, impaired social activities, depression and sleep disturbances.

Conclusion: The findings highlight the role and importance of Alzheimer’s disease in developing or intensifying the behavioral and psychological symptoms in adults with Down syndrome. Hence, an accurate assessment of Alzheimer's symptoms in adults with Down syndrome in order to facilitate the process of early diagnosis and timely intervention is essential.