Donald Edward Sweet, 66, a musculoskeletal pathologist who was a leading authority on diseases of the bones and joints, died Aug. 2 of kidney failure at his home in Ashton.

At the time of his death, Dr. Sweet was chairman and registrar of the department of bone and joint pathology at the Armed Forces Institute of Pathology (AFIP) in Washington. He had held that position since 1980.

He was internationally known for his expertise on bone disease and was often called on to give expert testimony in legal cases. He published hundreds of technical papers on pathology, contributed to books and research articles and often spoke at medical seminars.

As a medical educator, he directed the AFIP's annual course in orthopedic pathology and helped initiate a cooperative educational exchange with Canadian orthopedic surgeons and scientists.

Dr. Sweet was born in Norwalk, Conn., and graduated from Fairfield University in Connecticut. He received his medical degree from Georgetown University in 1963.

As a commissioned Army officer from 1968 to 1971, he served as a staff pathologist with the AFIP, which is part of the Walter Reed Army Medical Center. He attained the rank of major.

From 1971 to 1976, he taught pathology at the University of Virginia medical school. He rejoined the AFIP as a civilian employee in 1976, working first as assistant chief of the orthopedic pathology division before becoming chairman of the department of bone and joint pathology.

Dr. Sweet received awards from international medical organizations and the military for his contributions to pathology. He was a fellow of the College of American Pathologists.

He had lived in Ashton since 1976 and was a member of St. Louis Catholic Church in Clarksville.

Survivors include his wife of 39 years, Elizabeth Sweet, of Ashton; four children, Elizabeth Nichols of Silver Spring, Deborah LeNard of Falls Church, Christopher Sweet of Annandale and Dr. Kevin Sweet of Johnson City, Tenn.; and five grandchildren.