The top 5 health insurance providers based on membership are: UnitedHealthcare with over 50 million members Anthem Blue Cross with 41 million members Humana with 17 million members Centene with 15 million members Cigna Health with 15 million members The largest insurers overall are UnitedHealthcare, Anthem, Humana, Cigna and Aetna. But exact rankings fluctuate annually and regionally. Top Medicaid and Medicare insurers include Centene, Molina Healthcare and Anthem.