BACKGROUND: Incidental resection of parathyroid tissue is not uncommon during thyroidectomy and may occur even in the hands of experienced thyroid surgeons. We aimed to investigate the clinical relevance of incidental parathyroidectomy and to determine which risk factors are important for it. PATIENTS: Four hundred and forty consecutive patients with non-toxic multinodular goitre treated by total and near-total thyroidectomy were included prospectively in the present study. Patients in group 1 (n=48) had inadvertent resection of parathyroid gland, whereas patients in group 2 (n=392) did not have parathyroid glands removed. RESULTS: There was a positive correlation between the incidental parathyroidectomy and total thyroidectomy (r(s)=0.519, p=0.0001), and thyroid pathology (r(s)=0.338, p=0.0001) and intrathyroid parathyroid locations. Incidental parathyroidectomy did not have an impact on postoperative hypocalcemia. The risk for incidental parathyroidectomy was increased 13-fold for patients who underwent total thyroidectomy (OR: 13.7; 95% CI:4.08-46.05), 4-fold for patients with substernal goitre (OR: 4.1; 95% CI: 1.1-14.3). CONCLUSIONS: Total thyroidectomy, thyroid pathology, and intrathyroid parathyroid locations are risk factors for incidental parathyroidectomy. All established risk factors for incidental parathyroidectomy are also risk factors for postoperative hypocalcemia. Incidental parathyroidectomy during thyroid surgery may be a potential complication.