A 19-year-old motorcyclist was killed when he lost control of his bike in the Royal National Park at Waterfall on Saturday.
Police say the crash happened about midday when the man was riding with friends along McKell Avenue.
The man suffered critical injuries after he came off his bike and struck a roadside signpost. His friends rendered assistance until NSW Ambulance Paramedics arrived but the man, from Currans Hill, died at the scene.
McKell Avenue was closed for three and a half hours while investigators examined the scene.
A report will be prepared for the information of the NSW Coroner.
Police are urging anyone with information about this incident to call Crime Stoppers on 1800 333 000.