Background: Severe mental illness (SMI) is associated with increased cardiovascular risk. Dyslipidaemia is a potentially modifiable risk factor, which may be inadequately managed in patients with SMI. Objectives: To assess management of dyslipidaemia in patients with SMI versus healthy controls (HCs) in 2005 and 2015. Design and methods: Using Danish registers, we identified adult patients with SMI in the Greater Copenhagen Area (schizophrenia spectrum disorders or bipolar disorder) with ⩾1 general practitioner contact in the year before 2005 and 2015, respectively, and HCs without SMI matched on age and gender (1:5). Outcomes were lipid-profile measurements, presence of dyslipidaemia and redemption of lipid-lowering pharmacotherapy. Differences in outcomes between patients with SMI and controls were measured with multivariable logistic regression. Results: We identified 7217 patients with SMI in 2005 and 9939 in 2015. After 10 years, patients went from having lower odds of lipid measurements to having higher odds of lipid measurements compared with HCs [odds ratio (OR)₂₀₀₅ 0.70 (99% confidence interval (CI) 0.63–0.78) versus OR₂₀₁₅ 1.34 (99% CI 1.24–1.44); p_{2005versus2015} < 0.01]. Patients had higher odds of dyslipidaemia during both years [OR₂₀₀₅ 1.43 (99% CI 1.10–1.85) and OR₂₀₁₅ 1.23 (99% CI 1.08–1.41)]. Patients went from having lower odds of receiving lipid-lowering pharmacotherapy to having higher odds of receiving lipid-lowering pharmacotherapy [OR₂₀₀₅ 0.77 (99% CI 0.66–0.89) versus OR₂₀₁₅ 1.37 (99% CI 1.24–1.51); p_{2005versus2015} < 0.01]. However, among persons at high cardiovascular risk, patients had lower odds of receiving lipid-lowering pharmacotherapy during both years, including subsets with previous acute coronary syndrome [OR₂₀₀₅ 0.30 (99% CI 0.15–0.59) and OR₂₀₁₅ 0.44 (99% CI 0.24–0.83)] and ischaemic stroke or transient ischaemic attack (TIA) [OR₂₀₀₅ 0.43 (99% CI 0.26–0.69) and OR ₂₀₁₅ 0.61 (99% CI 0.41–0.89)]. Conclusion: These results imply an increased general awareness of managing dyslipidaemia among patients with SMI in the primary prophylaxis of cardiovascular disease. However, secondary prevention with lipid-lowering drugs in patients with SMI at high cardiovascular risk may be lacking.