Following reports at around 8.15am on Friday morning, police attended the scene on East Main Street, Armadale where a man was assaulted.
The injured man was traced by police officers and taken by ambulance to St John’s Hospital in Livingston.
Enquiries are ongoing to work out the nature of the attack.
A Police Scotland spokesperson said: "Around 8.15am on Friday, 19 March, officers were called to a report of a man assaulted in East Main Street, Armadale.
"Officers attended and traced the injured man.
"Enquiries ongoing and officers are following a definite line of enquiry."
Scottish Ambulance Service said: “We received a call today at 0818 hours to attend an incident in West Lothian.
"We dispatched one ambulance and a critical care paramedic to the scene. We transported one male patient in their 30s to hospital.”