BACKGROUND AND OBJECTIVES: The trend in detection rates of asymptomatic unruptured intracranial aneurysms (UIAs) on brain computed tomography angiography/magnetic resonance angiography (CTA/MRA) is not well established. Our objective was to evaluate time trends in asymptomatic UIA detection rates on brain CTA/MRA between 2005 and 2019. METHODS: We conducted a retrospective study of all brain computed tomography/magnetic resonance scans (n = 288 336 scans in 130 621 patients) performed between January 2005 and December 2019 at a tertiary referral hospital. Patients who underwent brain CTA/MRA examinations were included (n = 81 261 scans in 48 037 patients). The annual detection rate of new UIA cases was calculated based on the first brain CTA/MRA imaging. Detection rates were compared between three periods and across different age groups. RESULTS: The number of first CTA/MRA examinations increased significantly from 2005 to 2009 (n = 12 190 patients) to 2010-2014 (n = 14 969 patients) and 2015-2019 (n = 20 878 patients) (P <.001). The UIA detection rate also increased significantly from 1.7% in 2005-2009 to 2.5% in 2010-2014 and 3.4% in 2015-2019 (P <.001). The UIA detection rate increased significantly from 2010-2014 to 2015-2019 (relative risk [RR], 1.33; 95% CI, 1.17-1.51), particularly in patients aged 60-69 years (RR, 1.29; 95% CI, 1.01-1.63), 70-79 years (RR, 1.71; 95% CI, 1.30-2.25), and >79 years (RR, 2.33; 95% CI, 1.56-3.47). Furthermore, the detection rate of <5-mm UIAs increased from 2010-2014 to 2015-2019 (RR, 1.51; 95% CI, 1.28-1.77). CONCLUSION: The detection rate of asymptomatic UIAs, particularly in elderly patients, has increased significantly over the past 15 years, coinciding with the increased use of CTA/MRA imaging. Furthermore, the size of the identified UIAs has decreased. These findings raise concerns about the management strategies for UIAs, indicating the need for further research.