Thyroid stimulating hormone (TSH) serum levels in 16 elderly patients with outcomes of cerebral atherosclerosis and in 14 adult apparently healthy subjects have been analyzed. Samples of venous blood were drawn every 4 h during the same day, starting at 0000. Results were evaluated by “single cosinor”; and “population mean cosinor”; methods. In addition, chronodesms (time‐specified tolerance invervals) were computed. A statistically significant circadian rhythm of serum TSH has been detected only in adult healthy subjects, but not in elderly patients. These results are discussed considering: a) desynchronization within the group and/or of the single subject studied; b) age effect; c) the interference of the thyroid function in this disease.