Thyroid hormone deficiency may affect human speech and voice. The aim of this study was to evaluate speech variables in patients with hypothyroidism.A case control study.One hundred and twenty patients, 106 women and 14 men with symptoms and signs of thyroid failure; the diagnosis was confirmed by serum T410 mU/l. Eighty-eight normal subjects, 78 women and 10 men, age-, sex-, and smoking status- matched, served as controls.All symptoms and signs of hypothyroidism were recorded. Serum T4, T3, and TSH concentrations were measured. Speech parameters were analyzed by the Visipitch III system model 3900 and multidimensional voice program software and compared to a group of normal subjects with no thyroid disease.Mean age was 35.9±11.4 yr. Dryness in larynx and pharynx, dyspnea, and sensation of lump in the throat were reported by 53.49 and 43% of patients, respectively. Fundamental frequency, voice turbulence index, and soft phonation index were significantly different from control values. There was positive correlation between TSH concentration and variation in fundamental frequency and prevalence of voice disorders (37.2±31.2 vs 23.9±25.8 mU/l, p<0.003).Frequent speech disturbances occur in patients with primary hypothyroidism.