As of Sunday, at least 38 of those cases were in New York City, with at least three deaths believed to be linked to the illness reported statewide.
Officials say the majority of patients test negative for the novel coronavirus but positive for antibodies, indicating they had previously had COVID-19.
Related: What parents need to know about the mystery syndrome
Symptoms of PMSIS include persistent fever, rash, abdominal pain and vomiting.
Several other pediatric deaths are currently under investigation.
Health officials say they are still learning how the disease manifests.
New York is helping develop national criteria for identifying and responding to the syndrome at the request of the Centers for Disease Control and Prevention, Cuomo said.
New Jersey is reporting eight possible cases, but no deaths, while Yale New Haven Hospital in Connecticut has reported three cases.
Children elsewhere in the U.S. have also been hospitalized with the condition, which was also seen in Europe.
MORE CORONAVIRUS COVID-19 COVERAGE
COVID-19 Help, Information and Resources
UPDATES
Grieving the lost: Tri-State residents who have died
New York state
New Jersey
Connecticut
Long Island
RELATED INFORMATION
Share your coronavirus story with Eyewitness News
Stimulus check scams and other coronavirus hoaxes
Coronavirus prevention: how clean are your hands?
Centers for Disease Control and Prevention on coronavirus
Total count of NYC COVID-19 cases based on patient address