Background/Aim. There is an increasing need for evaluation of working ability due to lower level of social protection of workers and growing number of patients with mental diseases in Bosnia and Herzegovina (B&H). The aim of this study was to establish the influence of mental diseases on the occurrence of disability of I and III categories in B&H during the period from January 1st 2005 to December 31st 2006. Methods. This study involved 1 792 examinees with the complete loss of working ability (I disability category) (n = 921). Disability category III consisted of persons with limited working ability (n = 871). The instruments of research in this multricentric and retrospective study were the forms P-6 and D-2 for the years of service in B&H, and the form IN for persons with years of service abroad and personal features questionnaire (EPQ). Results. The study included 1 494 men (78.5%) and 298 women (21.5%). Univariant analysis represented very high statistical significance (p = 0.001) concerning: age (χ2 = 65.428), years of service (χ2=28.438), drinking (χ2 = 33.234), smoking (χ2=70.880), father’s education (χ2 = 58.124), migrations (χ2 = 14.874), sick leave (χ2 = 29.190), medical treatment (χ2 = 95.073) and rehabilitation (χ2 = 29.453). Multivariant analysis represented the influence on disability category I by parameters such as: years of service, sick leave, psychoticism and depression (p = 0.001). Hospital treatment and fatigation had influence on disability in both groups. Mental diseases are the leading cause in disability category I in 14.98% and in disability category III in 9.3% persons. Leading diseases in both disability categories were depression and schizophrenia followed by alcoholism, anxiety, brain organ psychosyndrome (BOPS) and other diseases. Conclusion. The following parameters have highest influence on the disability category: the years of service, sick leave, psychoticism, depression, and long-lasting disease, medical treatments and fatigation on the disability category III.