Background: Adults with congenital heart disease (ACHD) are at risk for stroke and dementia. We report baseline and Year 1 results from an ongoing study assessing brain health in people with moderate- and great-complexity ACHD. Methods: Participants aged ≥18 undergo baseline and Year-3 brain MRI/MRA and annual cognitive assessment (MoCA, NIH Toolbox-Cognitive Battery (NIH-TB)). Results: Of 93 participants to date, 79 (85%) have completed Year 1 follow-up. At baseline, the great-complexity group had lower MoCA (26.32 vs. 27.38; p=0.04) and NIH-TB scores (total composite 45.63 vs. 52.80; p=0.002) than the moderate-complexity group. Year-1 testing showed numerical improvements across cognitive batteries in both groups. More participants with great-complexity ACHD had white matter hyperintensities (WMH; 72% vs. 55%; p=0.21) and cerebral microbleeds (CMBs; 72% vs. 54%; p=0.17) on baseline neuroimaging, but differences were not significant. Conclusions: Baseline neuroimaging shows a greater-than-expected burden for age of CMB and WMH in the context of previous cardiac surgery. Baseline cognitive performance was worse with great-complexity ACHD. Improved cognitive battery performance across both subgroups at Year-1 suggests a practice effect. Repeat neuroimaging will be performed in Year-3 and cognitive performance is reassessed annually.