Hospital trusts in England each make an average of £950,000 a year from parking fees.
Over the past three years, NHS Foundation Trust hospitals made a total of £344 million from parking. Some of the highest earners brought in more than £10 million each in that time.
The report from motoring magazine Auto Express also revealed that trusts issued 275,000 fines to patients and visitors, worth an additional £2.8 million. This amounts to an average income of £8,200 each per year.
Fourteen per cent of trusts do not give any concessions to Blue Badge holders or long-term and terminally ill patients. While some hospitals set fees at the standard £3.50 per hour rate, others were found to go as low as 60p per hour.
The Department of Health said that more than half of NHS hospitals offer free parking, but it was found that, in most cases, this was for a maximum of 30 minutes. Only four trusts do not charge for parking.
The report, which was put together through a Freedom of Information request, found that a quarter of hospitals use the money for parking maintenance, with the remainder being used for patient care.
Katherine Murphy, chief executive of The Patients Association, said: "This is a tax on the ill." However, a British Parking Association spokeswoman said: ''Free parking at hospitals in Wales and Scotland has actually made the situation worse. If the users don't pay for the parking then the trust does."