We analysed the aetiology of hypothyroidism in 144 patients. In these hospital referral data, thyroid surgery and decompensated iodine deficiency were the major known causes of hypothyroidism (19.5% and 15.3% respectively), while in the majority of patients (45.14%) the aetiology was obscure. The idiopathic group had patients who were significantly younger (p less than 0.01), showed a gland size between 2 and 3 SD ranges in significantly higher preponderance (p less than 0.05), and presented with generally higher prevalence rates of signs and symptoms; however, only menstrual disturbances (p less than 0.01), loss/reduced appetite (p less than 0.01) and dry/thickened hair (p less than 0.25) reached statistical significance. Since hypothyroidism has definite and substantial morbidity, these results are of importance to public health and medical personnel for a Bayesian approach to the aetiological diagnosis of hypothyroidism and for ordering specific confirmatory laboratory investigations.