This study describes the duties and responsibilities of the medical physicist and estimates the number of medical physicists needed in the next decade. A questionnaire, sent to members of the American Association of Physicists in Medicine, was designed to cover: characteristics of medical physicists, nature of work in medical physics, distribution of effort, publications, administration and supervision, training of medical physicists, budget for medical physics, and regional medical programs. Following a tabulation of questionnaire results, a discussion concerning duties and responsibilities, estimate of manpower needs, certification and accreditation, and emerging areas of specialization for medical physicists are included. Recommendations suggest: (1) At least one full-time professional medical physicist is needed in each medical institution with more than 300 hospital beds. (2) Graduate training programs in medical physics shall terminate in a master or doctoral degree. In addition, experience shall be provided in clinical applications of pertinent subspecialities of physics. (3) Since projected needs would require doubling the number of medical physicists over the next 10 years, sufficient support of graduate training programs is essential. (4) Training programs in medical physics should be accredited. (5) Certification procedures for medical physicists need to be studied. (6) Courses on medical physics should be made available to premedical and medical students, as well as to paramedical students enrolled in schools of allied health sciences. (MJM)