Staff from nurses to the CEO have been suspended at a Nairobi hospital after the wrong patient underwent brain surgery.
One patient needed surgery for a blood clot on the brain, the other only non-invasive treatment for swelling.
But a horrifying mix-up of identification tags saw the wrong man operated on, reports say.
The doctors did not realise their mistake until "hours into the surgery", the Daily Nation reported.
They then realised "there was no blood clot".
The patient who was operated on is recovering, the hospital says, and an investigation is under way. Regulators have demanded a report and plan to hold a hearing.
Social media users have expressed shock that such an incident could have been allowed to happen.
It comes only six weeks after the health minister ordered an investigation into claims new mothers were sexually assaulted at the same hospital.
After the incident which took place last weekend came to light, Kenyatta National Hospital's CEO Lily Koros said the hospital "deeply regrets this event and has done all it can to ensure the safety and well-being of the patient in question".
"We are happy to inform the public that the patient is in recovery and progressing well," Ms Koros added.
She said four staff - the neurosurgeon, ward nurse, theatre receiving nurse and anaesthetist - had been suspended.
"The management has suspended the admission rights of a neurosurgery registrar and issued him with a show-cause letter for apparently operating on the wrong patient," Ms Koros said. A show-cause letter requires a staff member to account for his or her actions.
But the doctor's colleagues have protested against the suspension, reports The Star, arguing the person who put on the identification tag is the one that should be punished.
And hours later Kenyan Health Minister Sicily Kariuki said Ms Koros herself and and a clinical affairs officer were being sent home on compulsory leave while the affair was investigated.
Baffling blunder - Anne Soy, BBC News, Nairobi
Before an intrusive medical operation is carried out, a meticulous process of investigation, decision-making and preparation of the patient has to take place.
The medical profession has strict protocols to observe and information is verified at every stage.
No-one would expect the wrong skull to be opened up.
It has baffled many. Daniel Yumbya, the CEO of the Kenya Medical Practitioners and Dentists Board - the country's medical practice regulator - told me this case would be the first of its kind in the country.
The board has heard nearly 1,000 cases of medical malpractice in the last 20 years.
Mr Yumbya has written to the Kenyatta National Hospital demanding a comprehensive report on the incident, the files of both patients and statements from the medical practitioners in question.
Meanwhile, the doctors' union defended staff, saying the hospital was "overwhelmed" by staff shortages and inadequate operating theatre space.
"You find one doctor could be doing 10 to 19 operations [in a day]," Ouma Oluga, chief executive officer of the Kenya Medical Practitioners, Pharmacists and Dentists' Union, told Reuters news agency.
The Nation reports that - "in a miracle of some sort" - the two patients are in good condition. It adds that the person who had the blood clot might not need to undergo surgery after all, as his condition has improved significantly.
Social media users were scathing about the apparent error.
How do you conduct brain surgery on the wrong patient? Kenyatta National Hospital has outdone themselves. Horrfying!!!!— Carol Radull (@CarolRadull) March 1, 2018
Malaria, HIV, TB, and Kenyatta National Hospital are the leading causes of death in Kenya.— Joshua K. Njenga (@JKNjenga) March 2, 2018
Some called for the resignation of the hospital's entire board of management in light of the other controversies at the institution.
As well as the allegations that new mothers were sexually assaulted in the hospital, a woman was able to kidnap a newborn baby there in February. The baby was recovered and returned to his parents a day later.
The flagship national hospital has also been plagued with reports of broken equipment, overcrowding, and long waiting times for treatment. Its management blames insufficient funding and says inadequate health provision more widely in Kenya has placed an unreasonable burden on the hospital.