We set up a two-sided market framework to model competition between a Prefered Provider Organization (PPO) and a Health Maintenance Organization (HMO). Both health plans compete to attract policyholders on one side and providers on the other. The PPO, which is characterized by a higher diversity of providers, attracts riskier policyholders. Our two-sided framework allows us to examine the consequences of this risk segmentation on the providers' side, especially in terms of remuneration. The outcome of the competition depends mainly on two effects: a demand effect, influenced by the value put by policyholders on the providers access and an adverse selection effect, captured by the characteristics of the health risk distribution. If the adverse selection effect is too strong, the HMO receives a higher profit in equilibrium. On the contrary, if the demand effect dominates, the PPO profit is higher in spite of the unfavorable risk segmentation. We believe that by highlighting the two-sided market structure of the health plans' competition, our model provides a new insight to understand the increase in the PPOs' market share as observed in the USA during the last decade.