Aim To determine population-based incidence of conjunctival tumours in Olmsted County, Minnesota.

Methods The Rochester Epidemiology Project medical record linkage system was used to identify patients with conjunctival tumours in Olmsted County (1 January 1980 to 31 December 2015). Records were reviewed for demographics, types of tumours, histopathology, treatment and clinical course. Incidence rate of all tumours was calculated per 1 000 000 person-years. Poisson regression analysis was used to assess changes in incidence over time.

Results There were 504 patients with conjunctival tumours, giving an age-adjusted and sex-adjusted incidence rate of 125 per 1 000 000 (CI 113.5 to 135.5). Incidence increased over time (P<0.001). Most tumours (474, 94%) were benign. Of benign lesions, melanocytic lesions accounted for the majority (431, 86%), with adjusted incidence rates of 10.8 (CI 7.7 to 13.9) for complexion-associated melanosis, 49.7 (CI 42.9 to 56.6) for nevus and 44.1 (37.5–50.8) for primary acquired melanosis. Malignant lesions were rare (30, 6%) with 6 cases of melanoma, 21 cases of ocular surface squamous neoplasia (OSSN), 1 case of Langerhans cell histiocytosis and 2 cases of lymphoma. Adjusted incidence rates of conjunctival melanoma and OSSN were 1.5 (CI 0.3 to 2.8) and 6.1 (CI 3.5 to 8.7), respectively. Outcomes for melanoma (mean follow-up 14 years, range 0–34) and OSSN (mean follow-up 4 years, range 0–24) were favourable in 29 cases, with one fatality due to metastatic melanoma.

Conclusions In a population-based setting, most conjunctival tumours are benign, and the majority of lesions are melanocytic. While it is important to remain vigilant for malignancies, most conjunctival lesions in a community-based practice are not life-threatening.