Popular Sydney rails bookmaker Col Tidy has died after a long illness, a day before his 74th birthday.

Tidy scaled back his operation several years ago because of ill health and officially retired from the ring in 2011 when his eyesight failed.

He had been in the Prince of Wales Hospital for the past few weeks and died in the early hours of Monday morning.

Known affectionately as Coogee Col, Tidy was an old fashioned bookmaker who joined the modern era when he launched an online service with Mark Morrissey in 2001 and later sold it to Unibet for $20 million.

Tidy's biggest bet was a losing one when he famously let Belle Du Jour's owner John Singleton on to win $1 million on the filly in the 2000 Golden Slipper.

Belle Du Jour reared at the start and almost tossed Lenny Beasley from the saddle, coming out a clear four lengths last before staging a remarkable recovery to win.

Tidy was also a well-known owner and breeder with multiple Group One winning sprinter Zeditave and his daughter Ruffles among his best performed horses.