Updated on Oct. 10

The trial of Sutter Health, a sprawling system of 24 hospitals and 5,500 doctors is beginning on Thursday, over accusations that the major hospital group used its dominance in Northern California to stifle competition and force patients to pay higher medical bills.

Opening statements are scheduled in state court.

Sutter, the nonprofit hospital group in Sacramento, with operating revenues of $13 billion, has long been viewed as the classic example of a hospital system that got way too big. Its network of hospitals and services enabled it to essentially corner much of the market, corralling insurers and patients so that they couldn’t go elsewhere for less expensive or better treatment, according to a lawsuit filed by Xavier Becerra, the California state attorney general.

In bringing the case, Mr. Becerra cited research showing people in Northern California paid thousands of dollars more for certain hospital procedures than those in the southern part of the state.

While hospital care for a heart attack cost around $25,000 in San Francisco, it was closer to $15,000 in parts of Los Angeles. A doctor’s visit for a common cold cost $205 in San Francisco, compared to as low as $122 in Los Angeles.