Purpose: Previous studies have demonstrated handwriting changes in patients with overt hyperthyroidism due to Graves’ disease. The aim of the present study was to investigate handwriting features in patients affected by overt autoimmune hypothyroidism. Methods: Thirty subjects – 24 females and 6 males, mean and median age of 50.15 ± 16.8 years and 52.5 years, respectively – with overt hypothyroidism (OH) related to Hashimoto’s thyroiditis (Group 1), and 30 age- and sex-matched euthyroid individuals (Group 2) were recruited to write a “standard text”. Group 1 patients repeated the text once the euthyroid state was reached on L-T4 substitution therapy. Group 2 subjects wrote the text again 1 to 4 weeks thereafter. The letters underwent a detailed analysis by a handwriting expert, through inspection, a stereoscopic microscope and a magnifying glass. Furthermore, the time that both Groups took to go through with the text was clocked. Results: None of the handwriting variables differed significantly within each Group and between the two Groups. Hypothyroid patients took significantly more time to go through with the text compared to the time taken once they became euthyroid (3.29 ± 1.66 vs 2.63 ± 1.55 minutes, respectively) and the time taken by the control group (p < 0.01). Of note, three Group 1 patients missed to copy some words or even whole sentences on the paper while they were overtly hypothyroid. Conclusions: The present study demonstrates that handwriting speed is able to disclose the impact of thyroid hormone deficiency on the central nervous system's functions. In particular, the longer time taken to go through with the text and the sentences missed by some hypothyroid patients, are the counterpart of psychomotor slowdown, impaired attention and memory loss peculiar to OH.