The Reina Sofia Museum in Madrid has lost a 38-tonne steel sculpture by American artist Richard Serra, the museum said in a statement Wednesday.

The museum, one of the city's largest and most popular, commissioned the work - four stark, steel slabs - in 1986 and acquired it a year later for the equivalent of about $220,000 US.

After being exhibited, it was placed in a warehouse in 1990 with a company that specialized in storing large-scale artworks.

But that company was dissolved in 1998, said daily newspaper ABC. When the museum's director, Ana Martinez de Aguilar, decided a few months ago to display the sculpture again, no one could find it, the museum said.