The relationship between physical health and psychological wellbeing is a complex one, with each impacting upon the other to one degree or another. Psychiatric patients are often reported to be not as physically healthy as their counterparts in the general population, with reports of increased weight gain and decreased activity. This study of two classifications of psychiatric patients in a high security psychiatric establishment was an attempt to ascertain if such a relationship existed between physical fitness, psychopathology, weight gain and medication levels. Using standardized tests to assess two parameters of health-related fitness — Harpenden skinfold callipers to estimate percentage body fat (BF), and a submaximal cycle ergometer ride for aerobic capacity (VO2 max) — results were compared with the general population using the Allied Dunbar National Fitness Survey (Sports Council and Health Education Authority, 1992) as a reference. The results indicate significant differences in aerobic fitness between the two groups (P<0.01) and such differences could be a cause for concern and may constitute a threat to both physiological and mental wellbeing.