Objective: Pituitary adenomas (PA) are among the most common human neoplasms. To describe the epidemiology and assess the disease burden of clinically significant PAs, population-based studies are needed. Iceland has a small well-defined population. The aim of this study is to describe the epidemiology of PAs in Iceland over an expanded period of time. Design: This is a retrospective observational study, including all PAs diagnosed in Iceland from 1955 to 2012. Methods: Extensive clinical information was gathered in a database. Prevalence rates for all PA subtypes were calculated along with standardized incidence rates (SIR). Sex ratios and relationships with adenoma size, age, and symptoms were assessed. Results: We identified 471 individuals: 190 men and 281 women. Total prevalence in 2012 was 115.57/100 000, prolactinomas were most prevalent (54.37/100 000) followed by non-functioning adenomas (NFPAs) (42.32/100 000). Throughout the period, NFPAs were most common (43.0%) followed by prolactinomas (39.9%) and 11.3% had acromegaly and 5.7% Cushing's disease. Women are diagnosed younger with smaller adenomas. Total SIR has increased significantly and is now 5.8/100 000 per year. Conclusion: In this nationwide study spanning six decades, we have confirmed PAs rising prevalence and incidence rates noted in recent studies. We demonstrated higher overall prevalence and incidence rates than ever previously recorded with an increasing predominance of NFPAs, which is not explained by incidental findings alone. There is a relationship with the introduction of imaging modalities, but the vast majority of patients are symptomatic at diagnosis. This underlines the importance of increased awareness, education, and appropriate allocation of resources for this growing group of patients.