The life expectancy of adults with mental illness is worse than that of the general population and is largely due to poor physical health status. Physical activity has been consistently recommended for the prevention and management of many chronic physical health conditions and can also have benefits for mental health. This cross sectional study assessed the attitudes towards and preferences for physical activity among inpatient adults with mental illness, and differences by distress and gender. Self-report questionnaires were completed by 101 patients. Findings indicated that inpatient adults with mental illness are interested in doing physical activity while in hospital, primarily to maintain good physical health and improve emotional wellbeing. Fewer than half of participants agreed that physical activity has benefits for serious mental illness. Participants indicated a preference for walking and physical activity that can be done alone, at a fixed time and with a set routine and format. Major barriers were fatigue and lack of motivation. Females were more likely than males to prefer activities done with others of the same gender (P=0.001) and at the same level of ability (P<0.001). There were no significant differences by level of distress. These findings can inform physical activity intervention programming in hospital settings, which may contribute to decreasing the chronic disease burden and improve the psychological wellbeing in adults with mental illness.