Student in summer jazz program, Indiana University, 1962—1963. Student in summer jazz program, Michigan State University, 1963.
After a stint with Ira Sullivan (1962–64), he accompanied singers including Judy Garland, Barbra Streisand, Della Reese, Leslie Uggams, and Sheila Jordan between 1964 and 1970. He moved to New York City in 1966. In the 1970s Ditmas played with Joe Newman (1971), Jazz Interactions Orchestra (1971), Gil Evans (1971–77), Enrico Rava (from 1971), Stardrive, Atmospheres, Future Shock (1972), New Wilderness Preservation Band (1972–73), Paul Bley, Lee Konitz, Pat Metheny, Chet Baker (1974–75), and Stan Getz (1975).
Later in the 1970s he concentrated on solo performance, including experiments with drum machines. He returned to work with the Evans Orchestra from 1979 to 1985, and lived in Italy in 1986-87, where he played with Dino Saluzzi, Rava, Rita Marcotulli, and Pietro Tonolo. He played with his own trio D3 with Jack DeSalvo and Tony DeCicco from 1988.
D3 released Spontaneous Combustion on the Tutu label. In the 1990s he played with Pat Hall and Karl Berger among others. D3 reformed in 2008 and is currently performing as the D3 Standards Trio.
In 1990, Ditmas orchestrated the music to an opera by Patricia Burgess, The Dream of Four Directions. He also composed prolifically for film and television. Among his credits is the film Deathscape.
Married Patricia Burgess, June 20, 1987.