By Murray Weiss, Leslie Albrech

MANHATTAN — A doctor at one of the city's top hospitals was caught using a video camera to film up a woman's skirt on a southbound 4 train, prosecutors and sources said.

Urologist Adam W. Levinson, 39, was arrested Wednesday evening at the 14th Street-Union Square subway stop after good Samaritan Sheldon Birthwright spotted him using a tiny video camera clipped to a folded newspaper to film up a woman's skirt, according to sources and a criminal complaint filed with the Manhattan District Attorney's office.

"They say if you see something, say something," Birthwright, a retired Tranportation Security Admininistration employee, said. "I felt this guy needed talking to. I'm glad the police were there."

Levinson was arrested Wednesday about 5:15 p.m.. He was arraigned at Manhattan Criminal Court Thursday on charges of unlawful surveillance. He was released on $5,000 cash bail or $15,000 bond.

Birthwright was headed home from work at a Bronx construction site when the doctor caught his attention on the train. Levinson was holding a newspaper with a pen attached to it and moving it "in a suspicous manner" with his hand as he stood behind a woman, Birthwright said. When the woman moved, reading her Kindle, Levinson moved too.

"He looked to see if people were looking," Birthwright said. "But I knew he was filming her." The woman was oblivious to the fact that Levinson was filming her, Birthright said.

Birthwright, 46, followed Levinson off the train when he exited at 14th Street-Union Square and trailed him as he walked through the station, attempting to film the woman along the way, sources said. Birthwright flagged down transit detectives, but when they went to investigate Birthwright's claims, Levinson seemed to have disappeared in the rush hour crowd.

Minutes later, as Birthwright was waiting for the L train, he spotted Levinson again — standing at the bottom of the staircase with his camera aimed up women's skirts as they descended. Birthwright alerted two nearby cops and repeated his story. This time, the officers caught up with Levinson.

An officer investigated the pen-shaped device Levinson was carrying and found that it was in fact a camera and held "numerous clips" of similar material of women's undergarments, according to the criminal complaint.

Birthwright, who is an ordained minister with The New Life For Better Living Christian Center on Third Avenue, commended police for their quick reaction. He said Levinson was silent when cops arrested him.

"He's a doctor — it blows my mind," Birthwright said. "At Mt. Sinai Hospital. It's horrible. A perversion. Nasty. Who knows what he was doing."

Levinson is a urologist at Mt. Sinai Hospital who specializes in minimally invasive surgery, which can involve using small-scale cameras to explore inside patients' bodies. Urology is the study of the urinary tract.

Hospital spokesman Ian Michaels said the pen-style camera Levinson allegedly used to film the woman wasn't believed to be one of the scopes used in Levinson's medical work. Levinson has been suspended pending the outcome of the investigation, Michaels said. The highly regarded hospital was ranked 14th in the nation on U.S. News and World Report's 2012 "Best Hospitals" list.

Levinson, a 2001 graduate of New York Medical College, has won positive reviews on patient rating websites for his bedside manner and trustworthy demeanor. Levinson completed his urology sugery training at Columbia University, according to a biography on Mt. Sinai's website that was removed after news of his arrest spread.