Men and women are supposed to be kept apart on hospital wards to ensure dignity and privacy for patients.
But there were a large number of breaches at the hospitals, which are run by the Sandwell and West Birmingham NHS Trust, between January and August.
The total of 1,485 dwarfed that of other West Midlands hospitals.
There was not a single breach at Wolverhampton’s New Cross Hospital or Stafford’s County Hospital during the same period.
The figure also meant the Sandwell trust faced a fine of £371,250. However, fine enforcement is largely left to the discretion of clinical commissioning groups who don’t always impose them.
The trust confirmed it was fined £27,250 for the period between April and September, by which time the number of breaches had fallen sharply.
It comes just days after Sandwell trust chief executive Toby Lewis said pressure on its A&E was the worst he had seen in his 25-year career, with beds almost full and waits doubling.
There were 1,123 breaches in January alone, according to latest NHS figures, and the increase from the previous year was the highest in the country.
The breaches have continued during 2019 – there were 229 in February, 40 in March and 44 in July.
Hospital trusts are expected to take a "zero-tolerance" approach to mixed sex wards under NHS guidelines but a shortage of beds has led to this being ignored in Sandwell on many occasions.
Cases have been rare at other hospitals in the region.
The next highest was Russells Hall Hospital where there were 48 breaches between January and August. There were just two at Walsall Manor, both in January.
The Sandwell trust said it had made changes which it hoped would mean mixed sex breaches would reduce.
Chief operating officer Rachel Barlow said: "In 2019 we changed our local policies and for the six months from April to September 2019 had a handful of patients who spent time in a mixed area within one of our large, old open wards. For this we have been fined £27,250.
"In 2018 we had many more mixed sex breaches having applied a specific policy to assessment units within our trust, which we have since removed.
"We expect to continue to reduce breaches of this important standard, and a new hospital at Midland Met in 2022 will help us by giving us many more single, private rooms for our patients’ care.”