Aside from his subsequent fame derived from "Catcher," Salinger was also ironically well known for his reclusive nature, living in seclusion in Cornish, N.H. for more than 50 years. In spite of an injury sustained early last year, it's stated that Salinger died of natural causes.
From the article: "Despite having broken his hip in May," the agency said, "his health had been excellent until a rather sudden decline after the new year. He was not in any pain before or at the time of his death.""
Link to Original Source