The deinstitutionalization movement of the past 25 years has focused on the placement of people with mental retardation into community-based settings. There is a need for exercise- and health-related professionals to demonstrate a thorough understanding of the term mental retardation and all of the intellectual and behavioural ramifications that coexist with this condition before addressing the 'how to' of fitness evaluation. Therefore, the article outlines the range of intellectual and behavioural characteristics of this population, based on the level of retardation. Many researchers investigating body composition have reported that a disproportionate number of adults with mental retardation carry a percentage of body fat that would be considered unhealthy (e.g. it increases the risk of early onset of such diseases as hypertension and adult onset diabetes mellitus). Living arrangements (i.e. institution vs smaller residences) play a role in the prevalence of obesity. Many attempts of researchers to control weight in adults with mental retardation through caloric restriction, exercise, and a combination of diet and exercise, have had a varied outcome. Cardiovascular capacity is considered by most exercise physiologists as the major physiological indicator for overall fitness. The majority of researchers who have evaluated the cardiovascular fitness levels of adults with mental retardation have reported fitness levels representative of a very sedentary population. Therefore, one would expect a keen sense of urgency among researchers to develop training regimens targeted specifically for people with mental retardation. Many have been developed, but to date only 2 cardiovascular training regimens have been reported that specifically describe the necessary components of an exercise programme (i.e. frequency, duration, intensity) that would allow for reproducibility--a stationary bicycle routine using the Schwinn 'Air-Dyne' ergometer and a run/walk programme. Of these, only the programme using the Schwinn 'Air-Dyne' ergometer reported significant improvements in cardiopulmonary fitness. Researchers have demonstrated that: (1) body strength is valuable for recreation activities and activities of daily living; (2) competence in upper body muscular skills is a prerequisite for many available vocational opportunities; and (3) positive correlations have been established between muscular strength and industrial work performance in people with mental retardation. Therefore, there is a need for appropriate evaluation procedures for determining the muscular strength and endurance of people with mental retardation. The future directions for researchers and professionals concerned with the fitness status of people with mental retardation includes answering question such as: What will be the effect of obesity on general health status?(ABSTRACT TRUNCATED AT 400 WORDS)