PARIS — At the age of 71, Dr. Jacques Bérès, a veteran of war zones, left his comfortable Paris life last month to smuggle himself into Homs, the center of the Syrian revolt, to tend to the wounded and the sick.

Working in secret, in a dark, abandoned house, with only one operating table, three beds, four local aides and intermittent electricity, Dr. Bérès operated on 89 people, he said; all but nine survived.

Dr. Bérès, a surgeon who was part of the group that founded Médecins Sans Frontières, or Doctors Without Borders, appears to be the only Western doctor who has been able to enter Homs, where security forces have been carrying out a brutal assault. His account offers a rare glimpse at the medical emergency that has developed as the Syrian conflict rages on.

His journey into Syria began in early February when he crossed the Lebanese border with the help of smugglers, carrying luggage filled with medical equipment. He then traveled by car and motorbike to Al Qusayr, another besieged city that is part of Homs Province, where he worked for a few days with a Syrian doctor. When he finally made it to Homs, he spent about two weeks there.