A 14-year-old boy suffered serious head and leg injuries when he was hit by a car in Woodingdean.
He remains in a critical condition, according to police, who are appealing for information about the crash.
The accident happened shortly before 6pm in Warren Way and afterwards a 73-year-old man from Brighton was arrested on suspicion of drink driving.
Sussex Police said: “Emergency services were called to Warren Way, Woodingdean, Brighton, at 5.47pm on Monday (14 January) following a collision between a pedestrian and a Suzuki Alto car 60 metres west of its junction with Sandhurst Avenue.
“The pedestrian, a 14-year-old boy from Brighton, was taken to the city’s Royal Sussex County Hospital with serious head and leg injuries before later being transferred to Southampton General Hospital, where he remains in a critical condition.
“A 73-year-old Brighton man has been arrested on suspicion of drink driving, causing injury by dangerous driving and driving a vehicle without a licence.
“He has since been released under investigation.
“Anyone with information is asked to contact police by email at collision.appeal@sussex.pnn.