Apparently he had a secret surgery out in the ocean so nobody would find out. Why not tell anyone what was going on?
This is a particularly apt question given that issues related to presidential health are currently being discussed.
The information below is largely taken from The President Is a Sick Man: Wherein the Supposedly Virtuous Grover Cleveland Survives a Secret Surgery at Sea and Vilifies the Courageous Newspaperman Who Dared Expose the Truth by journalist Matthew Algeo*.*
First off, Grover Cleveland was the only American president to be elected in non-consecutive terms. He was sworn in for his second term in March of 1893. At the time, the country was dealing with a terrible depression along with an argument about whether the country should be on the gold standard or the silver standard. The fight caused the country to run into financial issues because of a law that required the purchase of silver based on certain criteria. Cleveland planned to fight for the repeal of this law by calling a special session of Congress in August 1893.
Soon after he took office, Cleveland discovered a rough patch on the roof of his mouth. Eventually this was discovered to be cancerous and the only way to stop its spread was for it to be removed. One of his aides worked to put together a surgical team in secret and the surgery was performed on a yacht in New York. In addition to the tumor, the team had to remove parts of his jaw and teeth. One of the doctors fashioned a device to fit inside Cleveland's mouth to replace the removed parts.
Cleveland basically made it through the surgery well and eventually would be able to return to normal work. However, the story began to leak out, but because of newspaper wars, the man most responsible for breaking the story was accused of lying and the story never really caught on.
As in other similar situations, Cleveland believed that the current financial situation required that his affliction be kept a secret to avoid further panic. At the time cancer was so feared that it seldom was referred to by name. In addition, Ulysses Grant had died of throat cancer not too many years before and his situation was well known to the public.
Cleveland also did not choose his own vice-president and while in the same party, the vice-president was on the opposite side of Cleveland's belief in the gold standard. Overall, he believed that he needed to keep it a secret.
We would see a similar situation in Woodrow Wilson's second term, where he would suffer a stroke that was almost completely kept a secret. There are other examples where the health of a president was largely hidden.