The BBC has learned that a patient has been diagnosed with cholera in the Cuban capital, Havana.
More than 50 people were infected and about 1,000 have received medical attention.
The authorities say the outbreak is under control but four hospitals are prepared to isolate patients.
They say people became ill after drinking water from contaminated（受污染的） wells.
But it is not clear what the source of the cholera is.
Most of the cases were in Cuba's south-eastern Granma province, more than 750km (470 miles) from Havana.
Hundreds of medical professionals from that area, including nurses, have worked and continue to work with patients in Haiti, where tens of thousands of people were infected after a devastating earthquake in 2010.
But the BBC's Sarah Rainsford says that for over a week doctors in Havana have been doing the rounds of their patients, checking for symptoms of cholera.
The infirm（衰弱的） , elderly and pregnant have been prioritised.
Now tests on a 60-year-old woman, admitted to hospital on Wednesday, have confirmed that she has the disease.
As she was diagnosed early, doctors say she is in a stable condition.
Health officials said they had "all the necessary resources to provide adequate attention to patients."
They said they had taken a series of measures, including taking samples of water and adding chlorine（氯） to purify it, to combat the outbreak.
Cholera is a bacterial infection that can cause severe diarrhoea（霍乱） and dehydration.
The Health Ministry said the last reported cholera outbreak on the island was soon after the 1959 Revolution.