STOCKHOLM (Reuters) - Melker Schorling, one of Sweden's most prominent investors, said on Monday he would leave his board roles next year, including the position of chairman at measurement technology firm Hexagon <HEXAb.ST>, due to health issues.

Schorling, 69, is chairman at his holding company MSAB <MELK.ST>, fat producer AAK <AAK.ST>, polymers group Hexpol <HPOLb.ST> and Hexagon, MSAB's biggest holding.

In a decade, MSAB, has had returns of over 500 percent, outperforming rivals such as Wallenberg-backed Investor AB <INVEb.ST> and Industrivarden <INDUa.ST>, leading Swedish media to dub Schorling the "King Midas" of the Stockholm bourse.

MSAB has a current market value of around 70 billion crowns.

At 0625 EDT, MSAB shares were down 3.4 percent, while Hexagon, the crown jewel of MSAB's portfolio corresponding to more than half of its net asset value, dropped 1.0 percent.

"It is of course with sadness that I have received the information of Melker Schorling’s worsening health condition,"

Hexagon chief Ola Rollen told Reuters in an e-mail, adding work with the company would continue with "business as usual".

With Rollen as CEO and Schorling as chairman and main owner, Hexagon has grown from a market value of just a few billion crowns at the turn of the century to its current market capitalization of more than 130 billion crowns ($14.58 billion).

"I will keep on driving Hexagon forward as CEO and Melker Schorling will continue as chairman until the annual general meeting this spring when we present our new chairman," Rollen said.

Hexpol shares rose 1.3 percent, while AAK dropped 1.2 pct.

MSAB's portfolio also include stakes in companies such as Assa Abloy <ASSAb.ST>, the world's biggest maker of locks, and Securitas <SECUb.ST>, the world's second-biggest provider of guards.

($1 = 8.9144 Swedish crowns)

(Reporting by Johannes Hellstrom; editing by Alistair Scrutton)