OBJECTIVES: Efforts to “bend the cost curve” in US health care need to be informed by a differentiated view of health care spending by disease.  We highlight the importance of particular diseases based on level and rate of growth of spending. METHODS: National health care spending by employers for all services and for prescription drugs was estimated using claims data from employer sponsored health plans from 2004 and 2008.  Data were projected using sampling weights derived from the Medical Expenditure Panel Survey and trends in spending were calculated as compound annual growth rates (CAGR).  Claims were assigned to disease-specific episodes using the Thomson Reuters Medical Episode Grouper (MEG). RESULTS: Annual spending data were analyzed for 122 employers with 11.5 million  covered lives in 2004 and 143 employers with 15.6 million covered lives in 2008.  Overall spending grew at 8.6% per annum while prescription drug spending grew at 10.8%.  Musculoskeletal conditions were the most important body system, representing 18% of all spending and growing at 11% per year, well above average.  Several specific conditions had total spending growth rates of 15%, including osteoarthritis of the spine, multiple sclerosis, and prostate cancer.  Preventive health services also grew at 15%.  The single disease with the largest total spending, angina pectoris, grew at less than 1% per year.  Drug spending grew the fastest for Crohn’s disease (25%), epilepsy (23%), and multiple sclerosis (19%).  Spending for type 2 diabetes drugs was particularly important, as it represented 11% of all drug spending and grew at 17% per year, well above average. CONCLUSIONS: Major drivers of recent growth in employer health care spending are conditions related to obesity, including musculoskeletal and endocrine conditions.  The highest rates of drug spending were observed in conditions where biologic therapies are becoming standard of care.