Increasing use of the emergency department (ED) is well documented, but little is known about the type and severity of ED visits or their distribution across safety-net and non-safety-net hospitals. We examined the rates of high-intensity ED visits--characterized by their use of advanced imaging, consultations with specialists, the evaluation of multiple systems, and highly complex medical decision making--by patients with a severe, potentially life-threatening illness in California from 2002 through 2009. Total annual ED visits increased by 25 percent, from 9.0 million to 11.3 million, but high-intensity ED visits nearly doubled, increasing 87 percent from 778,000 to 1.5 million per year. The percentage of ED visits with high-intensity care increased from 9 percent to 13 percent (a relative increase of 44 percent). Annual ED admissions increased by 39 percent overall; most of this increase was attributable to high-intensity ED admissions, which increased by 88 percent. Safety-net EDs experienced an increase in high-intensity visits of 157 percent, compared to an increase of 61 percent at non-safety-net EDs. These findings suggest a trend toward intensification of ED care, particularly at safety-net hospitals, whose patients may have limited access to care outside the ED.