According to Aon Hewitt, health maintenance organizationplans will have the highest premium increases in five years, as the average 2011 HMO rates increased 9.8 percent after plan changes, negotiations and terminations. This is the highest rate increase since 2006, when the rate grew 10 percent. In 2010, final rate increases were 9.4 percent and 9 percent in 2009.

High-deductible health plans and preferred provider organization plans, which typically have lower premiums than HMO, have become more widely used by employees over the last few years. This is especially true among employees who are young, single and overall healthy. However, HMOs usually provide greater benefits at a higher price. This tends to attract those who may use health care more frequently or require better coverage.

With this mix of HMO plan participants, there is a greater risk pool, which raises prices. Additionally, HMO plans are becoming more aggressive when predicting the cost impact of some upcoming health care reform provisions, such as covering children up to age 26, the elimination of certain lifetime and annual limits, and covering 100 percent of preventive care.