Aim: An incidental thyroid carcinoma (ITC) is a thyroid malignancy that is not clinically or cytologically detected preoperatively. The incidence of ITC is between 10% to 20% in the literature. A study was undertaken to assess the incidence of ITC in patients undergoing total thyroidectomy for benign disease of the thyroid to University Surgical Unit, North Colombo Teaching Hospital (NCTH), Sri Lanka. Materials and methods: Prospective cohort study was undertaken from November, 2002 to October, 2015. Patients with palpable thyroid nodules were assessed with fine needle aspiration cytology (FNAC) and ultrasound scan (USS) to ascertain benign thyroid disease (BTD). Hormone assays were conducted to detect thyroid status. All patients with BTD who underwent total thyroidectomy were included in the study. Histopathological assessments were made by a panel of pathologists. Patients with autoimmune thyroiditis (AIT) were excluded due to the known association with malignancy of the thyroid. Post-thyroidectomy histopathological diagnoses were collected prospectively and patients with ITC were identified. Statistical analysis was done using statistical package for the social sciences (SPSS) software, version 20. Results: Hundred and sixty seven patients (n = 167) who fulfilled the inclusion criteria were analysed (Male–20, female–147, median age = 40.25 year, range 28 year–62 year). ITC was found in 19 patients with an incidence of 11.38%. No significant association was noted with morphology, biochemical status of the thyroid or gender. Conclusion: Incidence of ITC is 11.38% in this cohort. Incidence of ITC being approximately 1:10 emphasizes the need to consider total thyroidectomy in the management of BTD.