There were about 3000American deaths.
According to some sources, the Imperial Japanese Navy lost approximately 2,155 sailors & airmen during the Battle of Midway.
However, according to Sawachi Hisae's "Midowei Kaisen: Kiroku", which tabulates the name, rank, birth province, age at time of death, and term of service (as compiled from Japanese prefectural records), there were exactly 3,057 Japanese casualties, including one civilian technician assigned to Soryu. This information is considered authoratative.
US casualties - 307
Japan casualties - Approximately 2,500.