- 2 updates
Lancashire Teaching Hospitals said the delays arose because of "intense" pressure on services last winter.
As a result some elective procedures were cancelled to enable staff to target urgent cases.
Health regulator Monitor has launched an investigation into why some patients are waiting too long for treatment at Lancashire Teaching Hospitals NHS Foundation Trust.
The trust provides services to patients at the Chorley and South Ribble Hospital, the Royal Preston Hospital and a Specialist Mobility and Rehabilitation Centre which works across the county.
Monitor said since April 2013 the trust had failed to see some patients within 18 weeks of them being referred by their GP.
Its inquiry will find out which services have been affected and whether the trust has breached its licence to provide healthcare services.