Thyroid function was assessed in 80 patients receiving long-term lithium therapy. Three of the 80 patients were biochemically hypothyroid and a further patient was receiving thyroxine for lithium associated hypothyroidism. A further eight patients had elevated TSH levels and eight patients had subnormal serum triiodothyronine levels. After a 24 month follow up period seven of the 80 patients have developed clinical hypothyroidism. One patient had elevated thyroid parameters and clinical features of mild hyperthyroidism. Additional clinical and laboratory data are included from seven patients with lithium associated hypothyroidism and three patients with lithium associated thyrotoxicosis who were not included in the survey population.