Enlargement of the thyroid is common, especially in areas of endemic iodine deficiency. Substernal enlargement of a goitre can cause compression of several mediastinal structures. As a consequence of tracheal compression and tracheomalacia, syndromes of chronic respiratory distress occur and intercurrent upper respiratory infections may lead to acute respiratory failure. Superior vena cava syndrome secondary to compression by a substernal goitre may be complicated by venous thrombosis. Although dysphagia is the most frequent oesophageal symptom of a substernal goitre, upper gastrointestinal bleeding from 'downhill' oesophageal varices may be an initial presentation. Arterial compression or thyrocervical steal syndrome by large substernal goitres occasionally cause cerebral hypoperfusion and stroke. Recurrent and phrenic nerve palsies, as well as Horner's syndrome, occur secondary to non-malignant mediastinal goitres and may resolve after surgery. Substernal goitres rarely cause therapy-resistant pleural effusions, chylothorax and pericardial effusion. In conclusion, although cervical goitres are easily recognised, the initial presentation of mainly substernal goitres may be unusual.