OBJECTIVES: To assess the extent of the treatment gap for mental disorders in the Czech Republic, determine factors associated with the utilization of mental health services and explore what influences willingness to seek mental health care. METHODS: Data from the CZEch Mental health Study, a nationally representative study of community-dwelling adults in the Czech Republic were used. The Mini International Neuropsychiatric Interview assessed the presence of mental disorders. 659 participants with current affective, anxiety, alcohol use and substance use disorders were studied. RESULTS: The treatment gap for mental disorders ranged from 61% for affective to 93% for alcohol use disorders. Mental health service use was associated with greater disability (OR 1.04; 95% CI 1.02-1.05; p < 0.001), female gender (OR 3.31; 95% CI 1.97-5.57; p < 0.001), urban residence (OR 1.84; 95% CI 1.12-3.04; p < 0.05) and a higher number of somatic diseases (OR 1.32; 95% CI 1.03-1.67; p < 0.05). Self-identification as having a mental illness was associated with greater willingness to seek a psychiatrist and a psychologist. CONCLUSIONS: The treatment gap for mental disorders is alarmingly high in the Czech Republic. Interventions to decrease it should target in particular rural areas, men and people with low self-identification as having a mental illness.