Shares in William Hill, the High Street bookmaker, have hit double the level at which they floated 18 months ago.
Thursday's rise to 450 pence gives the company a market value of £1.9bn.
The shares have climbed steadily since early 2003, pausing only last autumn while questions over the future of in-shop betting terminals were resolved.
Hill's has attributed rising profits to the rollout of betting terminals and new products including virtual greyhound racing and online poker.
The shares listed in June 2002 at 225p.
In late trading on Thursday, the shares slipped back a little to close at 448.5p.