Background :The behavioral phenotype in Down syndrome follows a characteristic pattern. Aims: To find the incidence of behavioral abnormalities in Down syndrome, to compare these findings with other causes of intellectual disability and normal population and to cluster these abnormalities. Settings :One hundred forty mentally challenged people attending at tertiary care set up and from various non-governmental organizations were included in the study. Patients from both rural and urban set up participated in the study. The age-matched group from normal population was also studied for comparison. Design :The study design is a cross-sectional survey done independently by four observers. Materials and Methods :A semi-structured proforma for demographic profile has been used. The behavioral abnormalities are assessed by using DASH II (Diagnostic Assessment for the Severely Handicapped second modified version) scale. Statistical Analysis :Demographic comparison has been done by analysis of variance. Correlation matrix has been run to identify correlation between individual items. Principal component analysis has been used for grouping the behavioral pattern. Results :Behavioral abnormalities as expected are more common in people having intellectual disability than the normal population. The Down syndrome group unlike other causes of intellectual disability shows higher scores in Stereotypy. Impulse control and Mania subscales. Factor analysis yields five characteristic factor structures, namely, hyperactive-impulsive, biological functions, affective, neurotic and organic-pervasive developmental disorder clusters. Conclusions :Contrary to the conventional belief of docile-fun and music loving prototype, individuals diagnosed with Down syndrome show clusters of behavioral abnormalities and management can vary depending on these target symptoms.