This study, reprinted from the Journal of Health Economics, uses simulation methods to quantify the effects of adverse selection. The data used to develop the model provide information about whether families can accurately forecast their risk and whether this forecast affects the purchase of insurance coverage--key conditions for adverse selection to matter. The results suggest that adverse selection is sufficient to eliminate high-option benefit plans in multiple choice markets if insurers charge a single, experience-rated premium. Adverse selection is substantially reduced if premiums are varied according to demographic factors. Adverse selection is also restricted in supplementary insurance markets. In this market, supplementary policies are underpriced because a part of the additional benefits that purchasers can expect is a cost to the base plan and is not reflected in the supplementary premium. As a result, full supplementary coverage is attractive to both low and high risks.