BOSTON (NYTIMES) - Acclaimed photographer Nicholas Nixon has retired from the Massachusetts College of Art and Design following allegations of inappropriate behaviour.

Nixon, 70, is perhaps best known for The Brown Sisters, a series of portraits documenting four sisters - one of whom is his wife - for 40 consecutive years.

He started taking them in 1975, the same year that he began a part-time professorship at MassArt.

Mr David Nelson, the college's president, said it had received allegations against Nixon, prompting it to start investigating whether he violated a law that prohibits discrimination on the basis of gender.

Nixon subsequently decided to retire.

The letter did not detail the nature of the allegations against Nixon. But in a statement reported by The Boston Globe, his lawyer indicated that the college is investigating reports that he allegedly made inappropriate comments to students and staff members.

The Brown Sisters is on display at the Institute of Contemporary Art in Boston.

Other photographs of his, which are often black and white and provide intimate looks into American life, have been collected by museums, including the Metropolitan Museum of Art, the National Gallery of Art and the Museum of Fine Arts in Boston.