Risk factors for recurrent laryngeal nerve (RLN) lesions after thyroid gland surgery were evaluated retrospectively in 1026 patients. RLN palsy occurred in 5.9 per cent; the incidence of permanent palsy was 2.4 per cent as 59 per cent of paralyses were transient. For euthyroid nodular goitre, Graves' disease, chronic lymphocytic thryoiditis, recurrent goitre and thyroid carcinoma, permanent nerve damage occurred in 1.7, 4, 5, 3.8 and 8 per cent of patients respectively. In relation to the number of nerves at risk, the incidence of permanent RLN palsy was 1.1 per cent for subtotal lobectomy and 4.0 per cent for total lobectomy. The overall incidence of permanent RLN palsy was 1.8 per cent of nerves at risk. There was no statistically significant difference between the number of RLN paralyses occurring after nerve exposure and that occurring after non-exposure in subtotal lobectomy, but in total lobectomy the permanent palsy rate increased from 3.8 to 7 per cent when the nerve was not exposed or identified (P<0.01). Underlying thyroid disease, the extent of resection and exposure of the nerve in total lobectomy are risk factors for both transient and permanent RLN palsy.