['Mild or subclinical hypothyroidism [raised thyroid-stimulating hormone (TSH) but normal free thyroxine (T4)] affects 5-10% of adults. Symptoms are non-specific and TSH levels are needed for diagnosis.', 'We explore the relationship between thyroid function and psychological distress and investigate the usefulness of an expert-designed Thyroid Symptom Questionnaire (TSQ) in identifying hypothyroidism.', 'DEPTH (DEPression and THyroid) is a cross-sectional study of 325 patients recruited from general practices in Bristol, for whom thyroid function tests were requested by the GP. Subjects completed the TSQ, General Health Questionnaire (GHQ-12) and Patient Health Questionnaire (PHQ) and had blood tests for TSH and free T4.', 'The mean age was 45.7 years; 252 subjects (78%) were female; median TSH was 1.6. Psychological morbidity in this population is high: 54.2% have a GHQ-12 score >3, indicating psychological distress. We found no relationship between TSH and psychological distress [adjusted odds ratio 1.02 (95% confidence interval 0.91-1.13), P = 0.78]. The prevalence of hypothyroidism was 6.2% (95% confidence interval 3.8-9.5%). We found no evidence of an unadjusted association between TSQ score and subclinical hypothyroidism [adjusted odds ratio of 1.09 (95% confidence interval 0.95-1.24), P = 0.23].'] Is investigation of thyroid dysfunction more likely in patients with high psychological morbidity?