What may be Philadelphia's last old-style X-rated movie theater has stopped showing films and may have gone out of business.

A handwritten sign on the door of the Forum Theater, 23d and Market Streets, reads, "Forum now closed." Neither the theater's owner, Anthony Trombetta, nor his attorney returned phone calls Thursday, but the closure appears to be a result of a dispute between Trombetta and his landlord, Richard Basciano.

In September, STB Investments Corp., which owns the property at 2208 Market St., filed suit in Municipal Court alleging the Forum had failed to pay about $29,000 in rent. Court filings show that STB moved to evict the Forum from the building where it had operated since 1975.

Once part of an extensive skid row on the western end of Center City, the Forum has struggled to stay in business at a time when pornographic fare has become easily available on the Internet. The city's two or three remaining porn theaters cater to a gay audience.

Meanwhile, the neighborhood around the Forum has grown more residential and affluent. Its neighbors now include the Murano condos, a new apartment house in the former AAA headquarters, and a new public high school.

In an effort to draw a broader clientele, Trombetta made an attempt in 2010 to transform the theater, which is not allowed to serve alcohol, into a full-service sex club. He initially won approval from the city Zoning Board of Adjustment to enlarge the building to accommodate a stage for live nude dancers and private rooms for one-on-one "booth sessions." Commonwealth Court overturned the zoning variance in 2011.