Dr. James Masterson, an internationally recognized psychiatrist who helped inaugurate a new approach to the study and treatment of personality disorders, including narcissism, died on April 12. He was 84 and lived in Rye, N.Y.

His death at a hospital in Greenwich, Conn., was from complications of pneumonia, his daughter, Nancy Masterson, said.

A trained psychoanalyst, Masterson was an authority on narcissistic and borderline personality disorders. At his death, he was clinical professor emeritus of psychiatry at Weill Medical College of Cornell University.

He was also the founder and director of the Masterson Institute for Psychoanalytic Psychotherapy. Established in 1977, the institute offers psychoanalytic training at its headquarters in Manhattan, its West Coast branch in San Francisco and, via the Internet, locations around the world.

Personality disorders affect millions of people in the United States alone. Patients with narcissistic personality disorder can be grandiose, attention-seeking and demanding. Those with borderline personality disorder tend toward self-destructiveness, manipulativeness and flash-flood anger.

Masterson was one of the first people to bring the psychoanalytic approach known as object relations theory to bear on the study of personality. In so doing, he helped widen the lens through which personality disorders are viewed beyond the classical Freudian one that analysts had favored for decades.

“The enormous contribution he made was in the understanding of personality disorders and the evolution of personality per se,” Allan Schore, a psychoanalyst and neuroscientist at the University of California, Los Angeles, said Thursday. “He really helped psychiatry shift to offer more complex, more effective models in the treatment of personality disorders.”

Most closely associated with the British psychoanalysts Donald Winnicott and Melanie Klein, object relations theory centers on infants’ early attachment to their mothers. This attachment is vital, the theory holds — so vital that disruptions can cause psychological disturbances later on.

Object relations theory was primarily meant to explain human behavior. But in work he began in the mid-20th century, Masterson came to believe that it also held the key to personality, in particular the origin and treatment of personality disorders. (The psychoanalysts Heinz Kohut and Otto F. Kernberg also played seminal roles in applying the object relations model to the realm of personality.)

Classical Freudianism roots personality disorders in the Oedipal period, roughly between the ages of 4 and 6. Applying the object relations model, Masterson placed the roots even farther back, between about 18 months old and 36 months old.

“The pre-Oedipal disorders, which include all the personality disorders by definition, are much more concerned with the issue of maternal availability,” Judith Pearson, director of the Masterson Institute’s East Coast division, said Thursday. “In the Oedipal phase, the conflict really includes the child’s rivalry with the same-sex parent for the love of the opposite-sex parent.”

With its emphasis on the Oedipal, the Freudian approach was ill suited to treating personality disorders, Masterson argued. He maintained that these disorders crucially involve the conflict between a person’s two “selves”: the false self, which the very young child constructs to please the mother, and the true self.

“The psychotherapy of personality disorders,” Pearson explained, “is an attempt is to put people back in touch with their real selves.”

Besides his daughter, Nancy, Masterson is survived by his wife, the former Patricia Cooke, whom he married in 1949; two sons, Jim and Richard; a brother, Richard; a sister, Joan Masterson; and three grandchildren.