Prison Health Services is moving to take on the greatest challenge in its history: a contract of nearly $100 million a year to care for 13,000 prisoners on Rikers Island and in other New York City jails. But as it does, some officials and others who have monitored the company's performance say it has occasionally failed to deliver quality care. 
The Tennessee-based company has grown enormously in recent years as it aggressively pursued a share of the nation's estimated $4.5 billion-a-year inmate health care market. And it has largely succeeded in cutting prison health costs for the governments it serves. 
But in Pennsylvania, Georgia, Florida, Maine and Washington, among others, it has been dogged at times by allegations of severe staffing problems, poor or unstable management and substandard care. 
In recent months in Cumberland County, Me., where the company is being replaced by local authorities, Prison Health Services routinely failed to provide inmates with prescribed medications or dental care, and nurses were sometimes asked to work 24-hour shifts, according to a sheriff's office report issued this month. 
The company's executives do not dispute that they have, at times, failed to live up to expectations. But they said that those troubled sites represented only a tiny share of the company's roughly 125 contracts, and they noted that there was no shortage of 
state and local governments who were pleased with their performance, including the states of Kansas and Indiana and Alameda County in the Oakland, Calif., region. 
The company and its corporate parent, America Service Group, which is traded on the Nasdaq, are based in Brentwood, Tenn. P.H.S. is scheduled to start work Jan, 1, assuming final negotiations are successful will receive extraordinary scrutiny here as it tries to improve what some already consider a seriously troubled system of inmate medical care. 
Three years ago, in an effort to cut costs, the city hired St. Barnabas Medical Center in the Bronx to handle all but the most severe inmate medical cases, paying the hospital a set fee per prisoner. While the city saved money, inmate complaints increased threefold after St. Barnabas took over, and the Manhattan district attorney opened a criminal investigation into problems with the care given to more than a dozen prisoners, including four who died. 
PHS will hire doctors, nurses and other staff members who will assess the health of inmates as they arrive and treat all but the most acute medical or mental health problems that arise. 
City officials acknowledged Prison Health's mixed reviews but said they were confident that the company could live up to their high expectations for the care to be provided at the Manhattan Detention Center and at clinics on Rikers Island and the Vernon C. Bain barge.