A California appeal court has ruled that for purposes of determining whether an employer is liable for an employee’s occupational disease or cumulative trauma injury, the date of injury is when the employee first suffered either temporary or permanent disability—not when medical treatment was received. The ruling is important because, with work-related disease or cumulative trauma, it can be difficult to ascertain the actual date of injury. That, in turn, may make it difficult to resolve which employer is liable when an individual has worked for multiple employers.