The objective of the study was to assess surgical strategy of papillary carcinoma of the thyroid based on residual tumour findings after completion thyroidectomy. We investigated the accuracy of intraoperative tumour classification in papillary thyroid cancers (PTC) and its effect on intraoperative decision-making. In a 34-year period, we performed 182 total thyroidectomies for PTC, 69 of which were completion thyroidectomies. The indications for completion thyroidectomy were (1) inaccurate assessment of the size of solitary tumours (n = 28), (2) unilateral (n = 23) and (3) bilateral multicentricity (n = 18). Fifteen patients had residual cancers (22%), which were significantly correlated with the extent of the first procedure. After initial lobectomy, residual tumours were present in 54% of patients, compared to only 3% after initial lobectomy, isthmusectomy and contralateral subtotal lobectomy. We favour lobectomy, isthmusectomy and contralateral subtotal lobectomy in patients with papillary thyroid cancers smaller than 1.5 cm in diameter and a total thyroidectomy in all other cases.