OBJECTIVE Postoperative hypocalcaemia has been reported to be more common after total thyroidectomy (TT) for Graves' disease than after TT for benign atoxic multinodular goitre (MNG). The reasons for this potential association are not clear. In the present study, the frequency and risk factors of hypocalcaemia after TT for Graves' vs MNG were compared. METHODS Between January 1999 and October 2009, patients with first-time surgery for Graves' disease or MNG treated with a TT were included in the study. Postoperative hypocalcaemia was defined by symptoms, calcium levels and treatment with calcium and/or vitamin D analogues during postoperative hospital stay, at discharge, and at the 6-week and 6-month follow-ups. Outcomes were compared with Mann-Whitney, chi(2) and Fishers' exact test where appropriate and by multivariable logistic regression analysis. RESULTS There were 128 patients with Graves' disease and 81 patients with MNG. Patients with Graves' disease were younger than patients with MNG (median age, 35 vs 51 years, p < 0.001). Symptoms of hypocalcaemia were more common in patients with Graves' disease (p < 0.001; OR, 95 % CI 3.26, 1.48-7.14), but the frequency of biochemical hypocalcaemia, postoperative levels of parathyroid hormone (PTH) and treatment with calcium and vitamin D did not differ between groups of patients. CONCLUSIONS Apart from more frequent symptoms of hypocalcaemia in patients with Graves' disease, there was no difference in the overall frequency of biochemical hypocalcaemia, low levels of PTH and/or treatment with calcium and vitamin D.