Objectives:
Comparison of the course of illness and functioning as well as occurrence of somatic diseases between patients with dual diagnosis, alcohol or drug addiction without mental disorders and patients with schizophrenia or affective disorders; drawing attention to the problems of people with dual diagnosis and importance of longer psychiatric inpatient treatment of this group of patients.

Methods:
108 persons were examined during inpatient psychiatric treatment. Injuries, occurrence of somatic diseases, aggressive behaviors, suicidal attempts, and discharges from hospital on patients’ request against medical advice were evaluated. Sociodemographic data and data associated with the course and treatment of an illness were compared between dual diagnosis group (n = 30), group of patients with mental illness (n = 41) and patients with alcohol or drug addiction (n = 37) using questionnaires designed by the authors.

Results:
In the dual diagnosis (DD) group, patients more often tried to commit suicide, started to use drugs or alcohol in younger age. In this group significantly more people were before marriage or after divorce. In the DD group and the group of patients with mental disorders (C), there were significantly more patients treated in hospitals longer than 180 days during their life. No statistically significant differences were found between groups when comparing incidence of somatic diseases, injuries, discharges from hospitals on patients’ request or aggressive behaviors.

Conclusions:
Due to non-compliance, frequent interruption of treatment, higher suicidal risk in the dual diagnosis group, there is a need of longer inpatient treatment in order to improve mental status, regular pharmacological treatment, provide social support, motivation, and prepare patients for psychotherapy of addiction. It is essential to take actions to create therapeutic standards of treatment and adjust financial funding for this group of patients in Poland.