Objectives: The aim of the study was to determine the prevalence and activity of root caries and its correlations with some clinical variables in people with the most common mental disorders. Study covered 120 randomly chosen hospitalized patients with selected mental disorders according to ICD-10 classification: mental and behavioural disorders due to alcohol use (ALH), schizophrenia and schizotypal disorders (SCH), mood, affective disorders (AF) in the respective age range of 35-44 years, as well as a comparative group comprising 52 mentally healthy participants. Methods: The severity of caries was evaluated by Root Caries Index (RCI) acc. Katz with regard to anatomical group and surface of upper and lower teeth, excluding third molars and prosthetic crowns. Statistical analysis was performed using Statistica 5.5 software. Associations between quantitative parameters were assessed by use of non-parametric Spearman test for significance of coefficient correlation. Results: Significantly higher prevalence of root caries ranged from 47,5% (ALH) to 68,75% (AF) and 64,58% (SCH), in comparison with control (p<0,01, chi-square test). Anterior teeth in the mandible were significantly less affected by caries. The mean RCI rates in the groups ALH, SCH, AF were 19,02±0,190SD, 24,87±0,206SD, 26,71±0,206SD respectively (control - 10,61±0,193SD). Results were significantly higher for all groups. (p<0,01, Mann-Whitney test). The Kruskall-Wallis test revealed insignificant differences within examined groups. A positive correlation was found between the RCI rate and duration of illness for patients with schizophrenic disorders (Spearman’s correlation coefficient r=0,330, p=0,021). The variable ‘number of hospital admissions’ was not correlated with the RCI in any of the groups. Conclusions: Institutionalized patients treated for mental disorders had high incidence and similar severity of root caries measured by RCI parameter. The duration of psychiatric disorder may influence increasing activity of root surface caries. Appropriate caries prevention programs should be realized in these instances.