Abnormalities of thyroid hormone status are common in severe psychiatric disorders. The purpose of this study was to stratify and compare thyroid hormone levels associated with schizophrenia and bipolar disorder and to evaluate their changes in the Latin American population. The study was retrospective. Statistical results were based on systematic analysis. A descriptive analysis of thyroid tests and clinical characteristics was performed. Thyroid function data were obtained from the records of 343 patients, 18 of whom were positive for anti-TPO. Abnormal thyroid hormone status in general and the presence of hypothyroidism and hyperthyroidism, in particular, were found in 29,3 %, 25,17 %, and 4,08 % of schizophrenia patients, respectively. There were no gender differences. Conclusions: Thyroid changes were found in patients with schizophrenia and bipolar affective disorder. These results highlight the importance of studying special populations with organic mental illnesses, such as schizophrenia, rather than focusing only on bipolar disorders, to achieve better characterization.