Nearly all the 50 top-performing funds between 1992 and 1997 had slipped down the rankings by the end of last year, according to Close Wealth Management.
Only three of the funds remained in the top 50 between 1997 and 2002. Of the remainder, the average ranking plummeted to 524th.
The biggest faller was Old Mutual's European Inc fund, which plunged from first position in 1992-97 to 1,174th. Scottish Widows Investment Partnership's UK smaller companies A fund slid from sixth to 1,130th.
Of the 47 funds which dropped out of the top 50, two slipped to rankings between 50th and 100th. Ten were ranked between 101st and 300th while 10 fell to between 301st and 500th.
Eleven funds dropped to between 501st and 700th while six slipped to between 701st and 900th. Eight fell to 900th position or below.
Chief executive Martin Smith says the findings show the importance of regularly monitoring investments. He says: “As many as two out of three investors have never reviewed their Isas and Peps, which is reflected by the fact that less than 1 per cent are transferred each year.
“Investors need to focus on the performance of their funds and, if they are not meeting expectations, they should be prepared to transfer them.”