Stereological studies have contributed with important results to the understanding of brain abnormalities in schizophrenia. The data obtained from stereological studies of brains from schizophrenic patients, including studies of the thalamus, hippocampus, and cortex, are discussed and suggest a central role of the thalamic nuclei in the etiology of the disease. The basic stereological tools are presented and possible biases in quantification studies are discussed.