The popular Simoncelli was killed at the 2011 Malaysian Grand Prix after he lost control and was hit by two bikes.
Romboni, 45, was taking part in the Sic Supermoto Day near Rome, when he was involved in an accident that bore tragic echoes of the one that claimed Simoncelli.
Reports say the rider ran onto the grass during a practice session but clung on to his bike, swerving back onto the track and into the path of former Italian champion Gianluca Vizziello who could do nothing to avoid colliding with Romboni.
The session was immediately stopped and Romboni flown by helicopter to hospital in the town of Latina. However, less than three hours after the incident, doctors announced Romboni's death.
The charity event, attended by other well known riders including former world champion Max Biaggi, was set to run throughout the weekend as a tribute to Simoncelli - nicknamed 'Sic' - who died aged 24 in October 2011.
Simoncelli suffered fatal injuries when, trying desperately to stay on his bike after running wide, he veered into the path of Italian compatriot Valentino Rossi and American Colin Edwards at the Sepang circuit.
Romboni competed between 1996-97 as an Aprilia factory rider in the 500cc category that is now MotoGP and was a race winner in the 125cc and 250cc categories. He also raced in World Superbikes.
(Photo: Doriano Romboni riding in 1994)