PURPOSE: To evaluate the prevalence and associated factors of reduced distance visual acuity (VA) and undercorrected refractive error in Finland in 2017. METHODS: A cross-sectional, nationwide health examination survey representing the Finnish adult population aged ≥18 years in 2017. Bilateral, habitual distance VA was measured in the survey. A pinhole test was performed for all participants with reduced VA, that is binocular distance VA logMAR ≥0.3 based on the initial letter chart test. Participants with an improvement of ≥5 letters using the pinhole were considered to have undercorrected refractive error, including also uncorrected errors. Multiple self-reported and register-based variables related to socio-demographic status, lifestyle, health-care use, health-related quality of life (HRQoL) and mental health were included in the survey, and their association with reduced VA and undercorrected refractive error was analysed using univariable logistic regression adjusted for age and sex as well as multivariable models. RESULTS: VA was measured from a total of 5937 (58%) survey participants, of which 184 had distance VA logMAR ≥0.3 with a population prevalence of 3.1%. Reduced VA was associated with older age, being single, having basic education only, limited/insufficient income, living in an urban setting, lower work ability, smoking, lower physical activity, lower consumption of vegetables and fruits, and worse HRQoL. A total of 110 (60%) participants showed a ≥5-letter improvement using a pinhole with a population prevalence of 1.8%. Among participants with logMAR ≥0.3, undercorrected refractive error was associated with younger age, better work ability, smoking, higher physical activity, a higher number of nurse visits and worse HRQoL. CONCLUSION: Reduced VA is associated with socio-demographic disadvantage and unfavourable lifestyle. Two out of three persons with reduced VA do not have their spectacles up to date. Inadequately corrected refraction seems to be a complicated phenomenon related to several factors deserving further study.