OBJECTIVE The aim of this study was to investigate the perceived level of internalized stigma among patients with severe mental illnesses and its relationship with demographic and clinical variables in Poland. METHODS A study sample (n=114, mean age=42.46±14.1 years; 55% of females) consisting of patients with nonorganic psychotic disorders as well as unipolar and bipolar affective disorders was evaluated (58% of outpatients and 39% of inpatients). All patients filled in the Internalized Stigma of Mental Illness (ISMI) scale (maximum severity=4). The demographic and clinical data were collected. RESULTS The study population demonstrated a mild level of internalized stigma (2.23±0.5). The highest score was observed in the alienation domain (2.63±0.8) and reflected moderate severity. The lowest score was noted in the stereotype endorsement domain (2.08±0.6). Moreover, the highest degree of internalized stigma was present in participants with unipolar affective disorder and was of moderate severity (2.46±0.6), while the level was moderate in the alienation domain (2.85±0.8). The level of vocational training education was the only variable associated with higher internalized stigma (P=0.02). There were no associations between gender, employment, and marital status and internalized stigma. The duration of the disease was the only clinical factor showing a significant positive correlation with stigma internalization (r=0.23; P=0.01). The number of hospital admissions and suicide attempts was not significantly correlated with internalized stigma. CONCLUSIONS People with severe mental illnesses in Poland experience a mild level of self-reported internalized stigma. Internalized stigmatization was most strongly associated with alienation, which indicates the need for stigma assessment procedures followed by stigma intervention programs in daily clinical practice. This is in accordance with the trend of environmental "open door" psychiatry, which could be the first step to decrease the level of stigma and internalized stigma in psychiatric patients in Poland.