The objective of this study was to examine young adults' healthcare utilisation and its possible association with health literacy. Many countries struggle with insufficient accessibility at emergency departments (EDs) and primary healthcare centres (PHCs). Young adults, aged 20-29 years old, account for a substantial number of unnecessary doctor visits where health literacy could be an explanatory factor. This study incorporated a combined retrospective and cross-sectional study design with analysis of registry data, including all registered outpatient doctor visits between 2004 and 2014 (n = 1 086 432), and strategic sample questionnaire data (n = 207), focusing on socio-demographics, symptoms and information-seeking behaviour. Mean differences between first-year and last-year doctor visits for each age group were calculated using registry data. Fischer's exact test was applied to questionnaire data to analyse group differences between ED and PHC visitors as well as between patients with sufficient health literacy and insufficient health literacy. Binary logistic regression was used to investigate covariation. Healthcare utilisation has increased among young adults during the past decade, however, not comparatively more than for other age groups. ED patients (n = 49) compared to PHC patients (n = 158) were more likely to seek treatment for gastrointestinal symptoms (P = 0.001), had shorter duration of symptoms (P = 0.001) and sought care more often on the recommendation of a healthcare professional (P = 0.001). Insufficient/problematic health literacy among young adults was associated with having lower reliance on the healthcare system (P = 0.03) and with a greater likelihood of seeking treatment for psychiatric symptoms (P = 0.002). Young adults do not account for the increase in healthcare utilisation during the last decade to a greater extent than other age groups. Young adults' reliance on the healthcare system is associated with health literacy, an indicator potentially important for consideration when studying health literacy and its relationship to more effective use of healthcare services.