A female passenger, also in her teens, was brought to Regional Hospital Mullingar with injuries understood to be non-life threatening.
Gardaí are appealing for witnesses following a serious single-vehicle e-scooter collision in Longford that has left one teenager in critical condition.
The crash happened on Battery Road at around 10:40pm on Friday night.
The male rider, who is in his late teens, was taken to Regional Hospital Mullingar before being transferred to Beaumont Hospital, where he remains in a critical condition.
A female passenger, also in her teens, was brought to Regional Hospital Mullingar with injuries understood to be non-life threatening.
Battery Road remains closed while Garda forensic collision investigators examine the scene, with local diversions in place.
Anyone with information, or travelling on Battery road between 10:15pm and 19:45pm with dash-cam footage, is asked to contact Longford Garda Station on (043) 335 0570, the Garda Confidential Line on 1800 666 111, or any Garda station.

Teenager Dies On E-Scooter Following Collision On Clare-Limerick Border
SSE Airtricity Customers To See Gas And Electricity Price Hikes From October
Russian Ambassador Says Irish Government "Cannot Be Treated As A Friendly One"
Two People Arrested In Connection With Shooting Near Dublin Shopping Centre
New Report Shows House Prices Are 17% Overvalued
Boy Dies After Train Collides With Car In Mayo
E-Scooter Ban For Under 18s Could Be In Place By October
Teenager Charged After Alleged Wrong-Way Driving Incident In Cork City